Directional display apparatus

ABSTRACT

A switchable privacy display comprises an emissive SLM, a parallax barrier, a switchable LC retarder, and passive retarders arranged between parallel output polarisers. In privacy mode, on-axis light from the SLM is directed without loss, whereas the parallax barrier and retarder layers cooperate to increase the VSL to off-axis snoopers. The display may be rotated to achieve privacy operation in landscape and portrait orientations. In public mode, the LC retardance is adjusted so that off-axis luminance is increased so that the image visibility is increased for multiple users. The display may also switch between day-time and night-time operation, for example for use in an automotive environment. A low reflectivity emissive display for use in ambient illumination comprises a SLM with emissive pixels, an absorptive parallax barrier and a high spectral leakage optical isolator. Head-on light from the pixels is directed with increased transmission efficiency while ambient light is strongly absorbed.

TECHNICAL FIELD

This disclosure generally relates to illumination from light modulationdevices, and more specifically relates to optical stacks for providingcontrol of illumination for use in display including privacy display andnight-time display.

BACKGROUND

Privacy displays provide image visibility to a primary user that istypically in an on-axis position and reduced visibility of image contentto a snooper, that is typically in an off-axis position. A privacyfunction may be provided by micro-louvre optical films that transmitsome light from a display in an on-axis direction with low luminance inoff-axis positions. However such films have high losses for head-onillumination and the micro-louvres may cause Moiré artefacts due tobeating with the pixels of the spatial light modulator. The pitch of themicro-louvre may need selection for panel resolution, increasinginventory and cost.

Switchable privacy displays may be provided by control of the off-axisoptical output.

Control may be provided by means of luminance reduction, for example bymeans of switchable backlights for a liquid crystal display (LCD)spatial light modulator. Display backlights in general employ waveguidesand edge emitting sources. Certain imaging directional backlights havethe additional capability of directing the illumination through adisplay panel into viewing windows. An imaging system may be formedbetween multiple sources and the respective window images. One exampleof an imaging directional backlight is an optical valve that may employa folded optical system and hence may also be an example of a foldedimaging directional backlight. Light may propagate substantially withoutloss in one direction through the optical valve whilecounter-propagating light may be extracted by reflection off tiltedfacets as described in U.S. Pat. No. 9,519,153, which is hereinincorporated by reference in its entirety.

BRIEF SUMMARY

According to a first aspect of the present disclosure there is provideda display device comprising: an emissive spatial light modulatorcomprising an array of pixels arranged in a pixel layer; a parallaxbarrier forming an array of apertures, wherein the parallax barrier isseparated from the pixel layer by a parallax distance along an axisalong a normal to the plane of the pixel layer; each pixel being alignedwith an aperture. The parallax barrier may direct light from each pixelinto a common viewing window. Advantageously a full resolution imagewith low reflectivity and reduced off-axis luminance may be achieved.

Along the direction in which the apertures are closest, the apertureshave a width a and the pixels have a width w that may meet therequirement that a≥w. Advantageously full luminance may be achieved inat least one viewing direction.

Along the direction in which the apertures are closest, the apertureshave a width a, the pixels have a pitch p and the pixels have a width wthat may meet the requirement that a≤(p−w/2). Advantageously theoff-axis luminance may be reduced to at most 50% for at least oneviewing direction.

The parallax barrier has a separation d from the pixels and the pixelshave a pitch p along the direction in which the apertures are closestand material between the parallax barrier and the pixels has arefractive index n that may meet the requirement that 2d/p≤√(2n²−1). Thedirection of minimum luminance may be at least 45 degrees toadvantageously achieve desirable off-axis luminance for a privacydisplay.

The parallax barrier has a separation d from the pixels and theapertures have a width a along the direction in which the apertures areclosest and material between the parallax barrier and the pixels has arefractive index n that may meet the requirement that d≥a√(n²−1)/2. Atmost 50% luminance is provided at a polar angle of 90 degrees toadvantageously achieve desirable off-axis luminance for a privacydisplay.

The parallax barrier has a separation d from the pixels and theapertures have a width a along the direction in which the apertures areclosest and material between the parallax barrier and the pixels has arefractive index n that may meet the requirement thatd≥an√(1−3/(4n²))/√3. At most 50% luminance is provided at a polar angleof 60 degrees to advantageously achieve desirable off-axis luminance fora privacy display.

The pitch p′ along the direction in which the apertures are closest maybe smaller than the pitch p of the respective aligned pixels along thedirection in which the pixels are closest; and the viewing window may beformed at a viewing window plane that is on the output side of thespatial light modulator. Advantageously luminance uniformity isincreased for a head-on display user.

The parallax barrier may form a two dimensional array of apertures, eachpixel being aligned with a respective aperture. Luminance reduction maybe achieved for lateral and elevation angles. Advantageously a privacydisplay may be provided with landscape and portrait privacy operation.Display reflectivity may be reduced and display efficiency in a head-ondirection increased.

The pixels may be arranged in columns and rows, the direction in whichthe apertures are closest may be at 45 degrees with respect to theelectric vector transmission direction of the output linear polariser;and each pixel may have a light emission region that is a square shapewith edges rotated by 45 degrees with respect to the electric vectortransmission direction of the output linear polariser. The apertures mayhave a square shape with edges rotated by 45 degrees with respect to theelectric vector transmission direction of the output linear polariser;or the apertures may have a circular shape. Advantageously uniformluminance roll-off and reduced luminance at high polar angles may beachieved along lateral and elevation azimuthal directions.

For at least some of the pixels the light emission region may compriselight emitting sub-regions and non-light emitting sub-regions. The ratioof the area of light emitting sub-regions to non-light emitting regionsmay be different for red, green and blue pixels. The colour pixels maybe driven with similar drive voltages to achieve matched outputluminance to those that are provided in displays for which the parallaxbarrier is not provided. Advantageously control and driver electronicshave reduced complexity and increased efficiency.

The parallax barrier may form a one dimensional array of apertures, thepixels being arranged in columns, each column of pixels being alignedwith a respective aperture. Modifications to pixel arrangements may bereduced, reducing cost. Each pixel may have a light emission region thatis extended in the direction in which the apertures are extended; thewidth of the red, green and blue light emission regions may be the samefor each of the pixels; and the height of the light emission regions maybe different for red, green and blue light emitting pixels. The displaymay conveniently be rotated about an axis one direction toadvantageously provide a comfortable viewing height for a head-onobserver. The yield and cost of alignment of the parallax barrier may bereduced.

The parallax barrier may be arranged to absorb light incident thereon.Display reflections may be reduced, advantageously increasing displaycontrast in brightly lit environments.

The absorption of the region of the parallax barrier between theapertures may be less than 100%, and may be greater than 80% preferablygreater than 90% and more preferably greater than 95%. The off-axisimage visibility of the display may be increased in comparison toparallax barriers that are provided with 100% absorption in absorbingregions.

The display device may be for use in ambient illumination and theparallax barrier may absorb at least some of the ambient illuminationtransmitted through the apertures that is reflected from the pixellayer. Reflections are reduced, advantageously increasing observed imagecontrast.

The display device may have one or more additional layers between thepixel layer and the parallax barrier, wherein the pixels, the one ormore additional layers and the parallax barrier may be formed as amonolithic stack. Advantageously the separation of the pixel layer andparallax barrier layer may be provided with high stability duringapplied mechanical forces.

The one or more additional layers may comprise at least one lighttransmitting inorganic layer arranged to provide a barrier to water andoxygen. The parallax barrier may comprise at least one lighttransmitting inorganic material that is arranged to provide a barrier towater and oxygen. The parallax barrier may be arranged between the pixellayer and at least one light transmitting inorganic layer that may bearranged to provide a barrier to water and oxygen. Advantageously thelifetime of the display may be increased.

An output polariser may be arranged on the output of the spatial lightmodulator, the output polariser being a linear polariser; and areflection control quarter-wave retarder may be arranged between theoutput polariser and spatial light modulator. Advantageously reflectionsfrom the pixel layer may be reduced.

The parallax barrier may be arranged between the pixel layer and thereflection control quarter-wave retarder. Advantageously a smallseparation between the pixel layer and the parallax barrier may beconveniently achieved.

The display device may further comprise an additional polariser arrangedon the output side of the output polariser, the additional polariserbeing a linear polariser; and at least one polar control retarderarranged between the output polariser and the additional polariser. Aprivacy display may be provided that advantageously has high visualsecurity level.

At least one of the output polariser and additional polariser, whencrossed with a notional polariser of the same material may havetransmission for wavelengths from 520 nm to 560 nm that is less than thetransmission for wavelengths from 450 nm to 490 nm. The transmission forwavelengths from 450 nm to 490 nm may be greater than 1%, preferablygreater than 2% and most preferably greater than 3%; and thetransmission for wavelengths from 520 nm to 560 nm may be less than 3%,preferably less than 2% and most preferably less than 1%. Thetransmission of the display may be increased in comparison to broadbandabsorbing polarisers. Advantageously display efficiency is increased.The transmission may be relatively greater for blue wavelengths.Advantageously the lifetime of the display may be increased.

The at least one polar control retarder may further comprise at leastone passive retarder.

The at least one polar control retarder may be capable of simultaneouslyintroducing no net relative phase shift to orthogonal polarisationcomponents of light passed by the output polariser along an axis along anormal to the plane of the at least one polar control retarder andintroducing a relative phase shift to orthogonal polarisation componentsof light passed by the reflective polariser along an axis inclined to anormal to the plane of the at least one polar control retarder. The atleast one passive retarder may comprise a retarder having its opticalaxis perpendicular to the plane of the retarder, the at least onepassive retarder having a retardance for light of a wavelength of 550 nmin a range from −150 nm to −900 nm, preferably in a range from −200 nmto −500 nm and most preferably in a range from −250 nm to −400 nm. Alarge off-axis polar region with reduced luminance may be achieved.Advantageously the visual security level is high for many snooperlocations.

The at least one retarder may comprise first and second quarter-waveplates arranged between the additional polariser and the outputpolariser, the first quarter-wave plate being arranged on the input sideof the second quarter-wave plate and being arranged to convert alinearly polarised polarisation state passed by the output polariser onthe input side thereof into a circularly polarised polarisation state,and the second quarter-wave plate on the output side being arranged toconvert a circularly polarised polarisation state that is incidentthereon into a linearly polarised polarisation state that is passed bythe additional polariser on the output side thereof, and at least oneretarder arranged between the pair of quarter-wave plates. The retarderarranged between the pair of quarter-wave plates may comprise a retarderhaving its optical axis perpendicular to the plane of the retarder, theat least one passive retarder having a retardance for light of awavelength of 550 nm in a range from −150 nm to −500 nm, preferably in arange from −200 nm to −400 nm and most preferably in a range from −250nm to −350 nm. A rotationally symmetric polar luminance reductionprofile may be provided. Advantageously a privacy display may beoperated in landscape and portrait modes. High visual security may beachieved for a snooper looking down from over a user's head.

The at least one polar control retarder may comprise a switchable liquidcrystal (LC) retarder comprising a layer of liquid crystal material andelectrodes arranged to apply a voltage for switching the layer of liquidcrystal material. The at least one polar control retarder may bearranged, in a first switchable state of the switchable liquid crystalretarder, simultaneously to introduce no net relative phase shift toorthogonal polarisation components of light passed by the reflectivepolariser along an axis along a normal to the plane of the at least onepolar control retarder and to introduce a net relative phase shift toorthogonal polarisation components of light passed by the reflectivepolariser along an axis inclined to a normal to the plane of the atleast one polar control retarder; and in a second switchable state ofthe switchable liquid crystal retarder, simultaneously to introduce nonet relative phase shift to orthogonal polarisation components of lightpassed by the reflective polariser along an axis along a normal to theplane of the at least one polar control retarder and to introduce no netrelative phase shift to orthogonal polarisation components of lightpassed by the reflective polariser along an axis inclined to a normal tothe plane of the at least one polar control retarder. Advantageously adisplay may be switched between privacy and public modes of operation.The region for which high visual security is provided to an off-axissnooper in privacy mode and high image visibility is provided to anoff-axis user in public mode is extended. A head-on user sees an imagewith high efficiency and high image visibility in both modes.

The display device may further comprise a reflective polariser arrangedbetween the output polariser and the at least one polar controlretarder, the reflective polariser being a linear polariser arranged topass the same linearly polarised polarisation component as the outputpolariser. A privacy display may be provided with high reflectivity in aprivacy mode of operation. In a privacy mode, the visual security levelmay be maintained for a wide range of ambient lighting conditions. In apublic mode the display reflectivity is reduced to achieve high imagevisibility for a wide range of viewing locations.

The output polariser may be a reflective polariser. Advantageouslydisplay efficiency may be increased. Display reflectivity may be reducedin comparison to displays with no parallax barrier.

The pixels may comprise light emitting diodes. Advantageously highluminous efficiency, high contrast and high luminance may be achievedwith wide colour gamuts.

The light emitting diodes may be organic light emitting diodescomprising an organic light emitting material. Advantageously thin androbust display may be provided. The thickness of the light emittingmaterial may be different for each of the red, green and blue lightemitting regions. The pixel sizes may be nominally the same for allcolours so that colour roll-off is substantially the same for all polarangles. The cost and complexity of drive electronics may be reduced.

At least some of the light emitting diodes may be inorganic micro lightemitting diodes. Advantageously very high luminance can be achieved.Barrier layers for water and oxygen may be omitted, advantageouslyreducing cost. Large areas may be provided between the micro-LEDs.Advantageously the reflectivity of the pixel layer may be reduced.Leaking polarisers may be provided for switchable privacy displays toachieve increased output efficiency.

The apertures have an absorption that may have a transmission gradientat the edges of the aperture that has a transmission gradient width ofgreater than 1 micron, preferably greater than 2 microns and morepreferably greater than 3 microns. Diffraction effects may be reduced toadvantageously achieve increased uniformity. Luminance roll-off profilesmay be provided with increased polar width to improve uniformity foroff-axis uses.

The array of apertures may be formed on a touch sensor electrode array.The at least one absorbing region of the parallax barrier may comprise atouch sensor electrode array. Advantageously low reflectivity touchelectrodes may be conveniently provided.

At least some of the apertures of the parallax barrier may comprise acolour filter. The apertures of the parallax barrier comprise an arrayof red, green and blue colour filters. Advantageously cross talk betweenadjacent pixels may be reduced. Colour gamut may be increased.

According to a second aspect of the present disclosure there is provideda method to form a display device comprising the steps of forming anarray of emissive pixels on a backplane by means of directing emissivematerials through a fine metal mask forming an encapsulation layer onthe array of emissive pixels comprising at least one transparentinorganic layer; forming the parallax barrier comprising an array ofapertures on the surface of the encapsulation layer by directing lightabsorbing material through a fine metal mask. Advantageously theparallax barrier may be formed using the same equipment used to form anOLED display, reducing cost.

According to a third aspect of the present disclosure there is provideda method to form a display device comprising the steps of forming anarray of emissive pixels on a backplane by means of directing emissivematerials through a fine metal mask forming an encapsulation layer onthe array of emissive pixels comprising at least one transparentinorganic layer; forming the parallax barrier comprising an array ofapertures on the surface of the encapsulation layer by means oflithographic patterning. Advantageously precise parallax barriers may beconveniently aligned with the pixel layer.

According to a fourth aspect of the present disclosure there is provideda reflectivity control display device for use in ambient illuminationcomprising the display device of the first aspect wherein the parallaxbarrier absorbs at least some of the ambient illumination.Advantageously output efficiency may be increased while displayreflectivity is maintained or reduced.

Any of the aspects of the present disclosure may be applied in anycombination.

Embodiments of the present disclosure may be used in a variety ofoptical systems. The embodiments may include or work with a variety ofprojectors, projection systems, optical components, displays,microdisplays, computer systems, processors, self-contained projectorsystems, visual and/or audio-visual systems and electrical and/oroptical devices. Aspects of the present disclosure may be used withpractically any apparatus related to optical and electrical devices,optical systems, presentation systems or any apparatus that may containany type of optical system. Accordingly, embodiments of the presentdisclosure may be employed in optical systems, devices used in visualand/or optical presentations, visual peripherals and so on and in anumber of computing environments.

Before proceeding to the disclosed embodiments in detail, it should beunderstood that the disclosure is not limited in its application orcreation to the details of the particular arrangements shown, becausethe disclosure is capable of other embodiments. Moreover, aspects of thedisclosure may be set forth in different combinations and arrangementsto define embodiments unique in their own right. Also, the terminologyused herein is for the purpose of description and not of limitation.

These and other advantages and features of the present disclosure willbecome apparent to those of ordinary skill in the art upon reading thisdisclosure in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example in the accompanyingFIGURES, in which like reference numbers indicate similar parts, and inwhich:

FIG. 1A is a schematic diagram illustrating in side perspective view aswitchable privacy display for use in ambient illumination comprising anOLED emissive spatial light modulator, parallax barrier, outputpolariser and reflection control quarter-wave retarder, reflectivepolariser, a switchable polar control retarder and an additionalpolariser arranged on the output side of the spatial light modulator;

FIG. 1B is a schematic diagram illustrating in front view alignment ofoptical layers in the optical stack of FIG. 1A;

FIGS. 2A and 2B are schematic diagrams illustrating in side views aparallax barrier for the privacy display of FIGS. 1A-B;

FIG. 3A is a schematic diagram illustrating in side perspective view thealignment of the parallax barrier with the pixels of FIG. 1A for anon-pupillated output;

FIG. 3B is a schematic diagram illustrating in side perspective view thealignment of the parallax barrier with the pixels of FIG. 1A for apupillated output;

FIG. 4 is a schematic diagram illustrating in top view an arrangement ofuniform emissive pixels and eye spot locations for various polar viewingangles;

FIG. 5 is a schematic diagram illustrating in top view an arrangement ofstructured emissive pixels and eye spot locations for various polarviewing angles;

FIG. 6 is a schematic diagram illustrating in side view the structure ofa spatial light modulator and aligned parallax barrier comprising upperingress reduction layers;

FIG. 7 is a schematic diagram illustrating in side view the structure ofa spatial light modulator and aligned parallax barrier comprising aglass cover layer;

FIGS. 8A, 8B, and 8C are schematic graphs illustrating the variation ofparallax barrier transmission with position for various parallax barrierstructures;

FIG. 9 is a diagram illustrating in perspective side view an arrangementof a switchable retarder in a public mode wherein the switchableretarder comprises a switchable LC layer with homogeneous alignment andcrossed A-plate polar control retarders;

FIG. 10A is a schematic diagram illustrating in side view propagation ofoutput light from a spatial light modulator through the optical stack ofFIG. 1A in a public mode of operation;

FIG. 10B is a schematic diagram illustrating in side view propagation oflight rays from an ambient light source through the optical stack ofFIG. 1A in a public mode of operation;

FIG. 10C is a schematic diagram illustrating in side view propagation ofoutput light from a spatial light modulator through the optical stack ofFIG. 1A in a privacy mode of operation;

FIG. 10D is a schematic diagram illustrating in side view propagation oflight rays from an ambient light source through the optical stack ofFIG. 1A in a privacy mode of operation;

FIG. 11A is a polar plot array for the component contributions andoutput of the arrangement of FIG. 1A comprising polar plots for spatiallight modulator luminance, parallax barrier transmission, switchableretarder transmission, switchable retarder reflection, public modeluminance, privacy mode luminance and visual security level for alux/nit ratio of 1.0;

FIG. 11B is a linear profile plot array for the component contributionsand output of the arrangements of FIG. 11A comprising linear profiles atazimuthal angles of 0 degrees (Eastern direction), 90 degrees (Northerndirection), 45 degrees (North Eastern direction) and 225 degrees (SouthWestern direction);

FIG. 11C is a polar profile plot and linear polar profile plot for theillustrative embodiment of FIGS. 11A-B with a lux/nit ratio of 0.25;

FIG. 12A is a polar plot array for the component contributions andoutput of the arrangement of FIG. 1A for an illustrative arrangement inwhich the parallax barrier is removed comprising polar plots for spatiallight modulator luminance, parallax barrier transmission, switchableretarder transmission, switchable retarder reflection, public modeluminance, privacy mode luminance and visual security level;

FIG. 12B is a linear profile plot array for the component contributionsand output of the arrangements of FIG. 12A comprising linear profiles atazimuthal angles of 0, 90, 45 and 225 degrees;

FIG. 13A is a polar plot array for the component contributions andoutput of the arrangement of FIG. 1A for an illustrative arrangement inwhich the switchable retarder is removed comprising polar plots forspatial light modulator luminance, parallax barrier transmission,switchable retarder transmission, switchable retarder reflection, publicmode luminance, privacy mode luminance and visual security level;

FIG. 13B is a linear profile plot array for the component contributionsand output of the arrangements of FIG. 13A comprising linear profiles atazimuthal angles of 0, 90, 45 and 225 degrees;

FIG. 14 is a schematic diagram illustrating in side view reflection ofambient light in the display of FIG. 1A;

FIG. 15 is a schematic graph illustrating the variation of outputluminance with wavelength for a broadband absorbing polariser and for aleaking absorbing polariser;

FIG. 16A is a schematic graph illustrating the variation of polarisertransmission with wavelength for a broadband absorbing polariser and fora leaking absorbing polariser and with respect to the spectral output ofred, green and blue emitting pixels for transmitted rays of FIG. 14 ;

FIG. 16B is a schematic graph illustrating the variation of reflectancewith wavelength for a broadband absorbing polariser and for a leakingabsorbing polariser and with respect to the spectral output of red,green and blue emitting pixels for reflected rays of FIG. 14 ;

FIG. 17A is a schematic diagram illustrating in side perspective view aswitchable privacy display for use in ambient illumination comprising amicro-LED emissive spatial light modulator, parallax barrier, outputpolariser and reflection control quarter-wave retarder, passive polarcontrol retarder, reflective polariser, a switchable polar controlretarder and an additional polariser arranged on the output side of thespatial light modulator;

FIG. 17B is a schematic diagram illustrating in front view alignment ofoptical layers in the optical stack of FIG. 17A;

FIG. 17C is a schematic diagram illustrating in top view an arrangementof micro-LED emissive pixels and eye spot locations for various polarviewing angles;

FIG. 17D is a schematic diagram illustrating in side perspective viewthe passive polar control retarder arranged between the output polariserand reflective polariser;

FIG. 18A is a schematic diagram illustrating in side view the structureof a spatial light modulator and aligned parallax barrier comprisingvignetted parallax barrier apertures;

FIGS. 18B, 18C, and 18D are schematic graphs illustrating the variationof parallax barrier transmission with position for various parallaxbarrier structures;

FIG. 19A is a polar plot array for the component contributions andoutput of the arrangement of FIG. 17A comprising polar plots for spatiallight modulator luminance, parallax barrier transmission, passive polarcontrol retarder, switchable retarder transmission, switchable retarderreflection, public mode luminance, privacy mode luminance and visualsecurity level;

FIG. 19B is a linear profile plot array for the component contributionsand output of the arrangements of FIG. 19A comprising linear profiles atazimuthal angles of 0, 90, 45 and 225 degrees;

FIG. 19C is a polar plot array for the component contributions andoutput of the arrangement of FIG. 17A comprising polar plots for spatiallight modulator luminance, parallax barrier transmission, passive polarcontrol retarder, switchable retarder transmission, switchable retarderreflection, public mode luminance, privacy mode luminance and visualsecurity level;

FIG. 19D is a linear profile plot array for the component contributionsand output of the arrangements of FIG. 19C comprising linear profiles atazimuthal angles of 0, 90, 45 and 225 degrees;

FIG. 20A is a polar plot array for the component contributions andoutput of the arrangement of FIG. 17A for an illustrative arrangement inwhich the parallax barrier is removed comprising polar plots for spatiallight modulator luminance, parallax barrier transmission, switchableretarder transmission, switchable retarder reflection, public modeluminance, privacy mode luminance and visual security level;

FIG. 20B is a linear profile plot array for the component contributionsand output of the arrangements of FIG. 20A comprising linear profiles atazimuthal angles of 0, 90, 45 and 225 degrees;

FIG. 21A is a polar plot array for the component contributions andoutput of the arrangement of FIG. 17A for an illustrative arrangement inwhich the switchable retarder and passive polarisation control retarderare removed and the parallax barrier provides transmission in the lightabsorbing regions; comprising polar plots for spatial light modulatorluminance, parallax barrier transmission, switchable retardertransmission, switchable retarder reflection, public mode luminance,privacy mode luminance and visual security level;

FIG. 21B is a linear profile plot array for the component contributionsand output of the arrangements of FIG. 21A comprising linear profiles atazimuthal angles of 0, 90, 45 and 225 degrees;

FIG. 21C is a polar plot array for the component contributions andoutput of the arrangement of FIG. 17A for an illustrative arrangement inwhich the switchable retarder and passive polarisation control retarderare removed and the parallax barrier provides no transmission in thelight absorbing regions; comprising polar plots for spatial lightmodulator luminance, parallax barrier transmission, switchable retardertransmission, switchable retarder reflection, public mode luminance,privacy mode luminance and visual security level;

FIG. 21D is a linear profile plot array for the component contributionsand output of the arrangements of FIG. 21A comprising linear profiles atazimuthal angles of 0, 90, 45 and 225 degrees;

FIG. 22A is a diagram illustrating in perspective side view anarrangement of a switchable retarder in a privacy mode wherein theswitchable retarder comprises a switchable LC layer with homogeneousalignment arranged between C-plate passive polar control retarders;

FIG. 22B is a diagram illustrating in perspective side view anarrangement of a switchable retarder in a public mode wherein theswitchable retarder comprises a switchable LC layer with homogeneousalignment arranged between C-plate passive polar control retarders;

FIG. 23A is a schematic diagram illustrating in perspective side view anarrangement of retarder layers arranged between parallel polarisers andcomprising a 270 degree super twisted switchable liquid crystal retarderarranged between quarter-wave plates;

FIG. 23B is a polar plot array for the component contributions andoutput of the arrangement of FIG. 23A comprising polar plots for spatiallight modulator luminance, parallax barrier transmission, switchableretarder transmission, switchable retarder reflection, public modeluminance, privacy mode luminance and visual security level;

FIG. 23C is a linear profile plot array for the component contributionsand output of the arrangements of FIG. 23B comprising linear profiles atazimuthal angles of 0, 90, 45 and 225 degrees;

FIG. 24A is a schematic diagram illustrating in perspective views theappearance of luminance of a mobile device in public mode comprising thedisplay of FIG. 1A with polar control retarder of FIG. 23A withappearance shown in order from top left clockwise: head-on landscape,head-on portrait, look-down portrait and look-from-right landscape;

FIG. 24B is a schematic diagram illustrating in perspective views theappearance of luminance of a mobile device in privacy mode comprisingthe display of FIG. 1A with polar control retarder of FIG. 23A withappearance shown in order from top left clockwise: head-on landscape,head-on portrait, look-down portrait and look-from-right landscape;

FIG. 24C is a schematic diagram illustrating in perspective views theappearance of reflectivity of a mobile device in privacy mode comprisingthe display of FIG. 1A with polar control retarder of FIG. 23A withappearance shown in order from top left clockwise: head-on landscape,head-on portrait, look-down portrait and look-from-right landscape;

FIG. 25A is a schematic diagram illustrating in top view an automotivevehicle with a switchable directional display arranged within thevehicle cabin in a night mode of operation;

FIG. 25B is a schematic diagram illustrating in side view an automotivevehicle with a switchable directional display arranged within thevehicle cabin in a night mode of operation;

FIG. 26 is a schematic diagram illustrating in side perspective view aswitchable privacy display for use in ambient illumination comprising anOLED emissive spatial light modulator, one dimensional parallax barrier,output polariser and reflection control quarter-wave retarder, areflective polariser, a switchable polar control retarder and anadditional polariser arranged on the output side of the spatial lightmodulator;

FIG. 27 is a schematic diagram illustrating in front view alignment ofoptical layers in the optical stack of FIG. 26 ;

FIG. 28 is a schematic diagram illustrating in side perspective view aswitchable privacy display for use in ambient illumination comprising amicro-LED emissive spatial light modulator, parallax barrier, and outputpolariser that is a reflective polariser, reflection controlquarter-wave retarder, a switchable polar control retarder and anadditional polariser arranged on the output side of the spatial lightmodulator;

FIG. 29 is a schematic diagram illustrating in side view reflection ofambient light in the display of FIG. 28 ;

FIG. 30 is a schematic diagram illustrating in side perspective view alow reflectivity display for use in ambient illumination comprising anOLED emissive spatial light modulator, two dimensional parallax barrier,leaking output polariser and reflection control quarter-wave retarderarranged on the output side of the spatial light modulator;

FIG. 31 is a schematic diagram illustrating in side view reflection ofambient light in the display of FIG. 30 ;

FIG. 32 is a schematic diagram illustrating in side perspective view atouch screen low reflectivity display for use in ambient illuminationcomprising an OLED emissive spatial light modulator, two dimensionalparallax barrier comprising touch sensor electrode layers, leakingoutput polariser and reflection control quarter-wave retarder arrangedon the output side of the spatial light modulator;

FIG. 33 is a schematic diagram illustrating in front view reflection ofambient light in the display of FIG. 32 ;

FIG. 34 is a schematic diagram illustrating in side view the structureof FIG. 32 ;

FIG. 35A is a schematic diagram illustrating in side perspective view alow reflectivity display for use in ambient illumination comprising anOLED emissive spatial light modulator, two dimensional parallax barrierand no output polariser arranged on the output side of the spatial lightmodulator;

FIG. 35B is a schematic diagram illustrating in side view reflection ofambient light in the display of FIG. 35A;

FIG. 36A is a schematic diagram illustrating in side perspective view alow reflectivity display for use in ambient illumination comprising anOLED emissive spatial light modulator, two one dimensional parallaxbarriers and no output polariser arranged on the output side of thespatial light modulator;

FIG. 36B is a schematic diagram illustrating in side view reflection ofambient light in the display of FIG. 36A;

FIG. 37A is a schematic diagram illustrating in side view a catadioptricoptical element array arranged between the pixels of the spatial lightmodulator and the parallax barrier;

FIG. 37B is a schematic graph illustrating the variation of outputluminance with polar angle for the arrangement of FIG. 37A;

FIGS. 38A, 38B, 38C, and 38D are schematic diagrams illustrating in sideviews a method to manufacture a parallax barrier for an emissive displayusing a fine metal mask;

FIGS. 39A, 39B, 39C, 39D, 39E, and 39F are schematic diagramsillustrating in side views a method to manufacture a parallax barrierfor an emissive display using lithography;

FIGS. 40A, 40B, 40C, and 40D are schematic diagrams illustrating in sideviews a method to manufacture a parallax barrier for an emissive displayusing printing;

FIG. 41 is a schematic diagram illustrating in side perspective view aswitchable privacy display for use in ambient illumination comprising anOLED emissive spatial light modulator comprising profiled OLED pixels,output polariser and reflection control quarter-wave retarder,reflective polariser, a switchable polar control retarder and anadditional polariser arranged on the output side of the spatial lightmodulator;

FIG. 42 is a schematic diagram illustrating in side perspective viewpixels of an OLED emissive spatial light modulator wherein the OLEDpixels are profiled OLED pixels comprising profiled wells and a highindex filler material;

FIG. 43 is a schematic diagram illustrating in side view one pixel of anOLED emissive spatial light modulator wherein the OLED pixel comprisesprofiled wells and a high index filler material;

FIG. 44 is a schematic graph illustrating variation of luminousintensity for profiled and non-profiled OLED pixels;

FIG. 45A is a polar plot array for the component contributions andoutput of the arrangement of FIG. 41 comprising polar plots for spatiallight modulator luminance, switchable retarder transmission, switchableretarder reflection, public mode luminance, privacy mode luminance andvisual security level;

FIG. 45B is a linear profile plot array for the component contributionsand output of the arrangements of FIG. 45A comprising linear profiles atazimuthal angles of 0, 90, 45 and 225 degrees;

FIG. 46 is a schematic diagram illustrating in side perspective view aswitchable privacy display for use in ambient illumination comprising anemissive spatial light modulator, a parallax barrier, a first polarcontrol retarder arranged between the display polariser of the emissivespatial light modulator and a first additional polariser; and areflective polariser and second polar control retarder arranged betweenthe first additional polariser and a second additional polariser;

FIG. 47A is a schematic diagram illustrating in front perspective viewan arrangement of polarisers and polar control retarders for theembodiment of FIG. 46 wherein the first and second polar controlretarders are crossed;

FIG. 47B is a graph illustrating a simulated polar profile of luminanceoutput of an emissive spatial light modulator without the barrierstructure;

FIG. 47C is a graph illustrating a simulated polar profile oftransmission of the barrier structure of light from the pixels of theemissive spatial light modulator;

FIG. 47D is a graph illustrating a simulated polar profile oftransmission of the second polar control retarder of FIG. 47A arrangedbetween the first and second additional polarisers wherein the electricvector transmission directions of the polarisers are parallel;

FIG. 47E is a graph illustrating a simulated polar profile ofreflectivity of the second polar control retarder of FIG. 47A arrangedbetween a reflective polariser and the second additional polariserwherein the electric vector transmission directions of the polarisersare parallel;

FIG. 47F is a graph illustrating a simulated polar profile of the totalreflectivity comprising the reflectivity of FIG. 47E and the Fresnelreflectivity from the front surface of the display device;

FIG. 47G is a graph illustrating a simulated polar profile oftransmission of the first polar control retarder of FIG. 47A arrangedbetween the display polariser and the first additional polariser whereinthe electric vector transmission directions of the polarisers areparallel;

FIG. 47H is a graph illustrating a simulated polar profile of thelogarithm of total output luminance of the spatial light modulator andfirst and second polar control retarders of FIG. 47A;

FIG. 47I is a graph illustrating a simulated polar profile of thesecurity level, S of the arrangement of FIG. 47A in privacy mode for anambient illuminance measured in lux that is twice the head-on displayluminance measured in nits; and

FIG. 47J is a graph illustrating a simulated polar profile of thesecurity level, S of the arrangement of FIG. 47A in public mode for anambient illuminance measured in lux that is twice the head-on displayluminance measured in nits.

DETAILED DESCRIPTION

Terms related to optical retarders for the purposes of the presentdisclosure will now be described.

In a layer comprising a uniaxial birefringent material there is adirection governing the optical anisotropy whereas all directionsperpendicular to it (or at a given angle to it) have equivalentbirefringence.

The optical axis of an optical retarder refers to the direction ofpropagation of a light ray in the uniaxial birefringent material inwhich no birefringence is experienced. This is different from theoptical axis of an optical system which may for example be parallel to aline of symmetry or normal to a display surface along which a principalray propagates.

For light propagating in a direction orthogonal to the optical axis, theoptical axis is the slow axis when linearly polarized light with anelectric vector direction parallel to the slow axis travels at theslowest speed. The slow axis direction is the direction with the highestrefractive index at the design wavelength. Similarly the fast axisdirection is the direction with the lowest refractive index at thedesign wavelength.

For positive dielectric anisotropy uniaxial birefringent materials theslow axis direction is the extraordinary axis of the birefringentmaterial. For negative dielectric anisotropy uniaxial birefringentmaterials the fast axis direction is the extraordinary axis of thebirefringent material.

The terms half a wavelength and quarter a wavelength refer to theoperation of a retarder for a design wavelength λ₀ that may typically bebetween 500 nm and 570 nm. In the present illustrative embodimentsexemplary retardance values are provided for a wavelength of 550 nmunless otherwise specified.

The retarder provides a phase shift between two perpendicularpolarization components of the light wave incident thereon and ischaracterized by the amount of relative phase, F, that it imparts on thetwo polarization components; which is related to the birefringence Δnand the thickness d of the retarder byΓ=2.π.Δn.d/λ ₀  eqn. 1

In eqn. 1, Δn is defined as the difference between the extraordinary andthe ordinary index of refraction, i.e.Δn=n _(e) −n _(o)  eqn. 2

For a half-wave retarder, the relationship between d, Δn, and λ₀ ischosen so that the phase shift between polarization components is Γ=π.For a quarter-wave retarder, the relationship between d, Δn, and λ₀ ischosen so that the phase shift between polarization components is Γ=π/2.

The term half-wave retarder herein typically refers to light propagatingnormal to the retarder and normal to the spatial light modulator.

Some aspects of the propagation of light rays through a transparentretarder between a pair of polarisers will now be described.

The state of polarisation (SOP) of a light ray is described by therelative amplitude and phase shift between any two orthogonalpolarization components. Transparent retarders do not alter the relativeamplitudes of these orthogonal polarisation components but act only ontheir relative phase. Providing a net phase shift between the orthogonalpolarisation components alters the SOP whereas maintaining net relativephase preserves the SOP. In the current description, the SOP may betermed the polarisation state.

A linear SOP has a polarisation component with a non-zero amplitude andan orthogonal polarisation component which has zero amplitude.

A linear polariser transmits a unique linear SOP that has a linearpolarisation component parallel to the electric vector transmissiondirection of the linear polariser and attenuates light with a differentSOP.

Absorbing polarisers are polarisers that absorb one polarisationcomponent of incident light and transmit a second orthogonalpolarisation component. Examples of absorbing linear polarisers aredichroic polarisers.

Reflective polarisers are polarisers that reflect one polarisationcomponent of incident light and transmit a second orthogonalpolarisation component. Examples of reflective polarisers that arelinear polarisers are multilayer polymeric film stacks such as DBEF™ orAPF™ from 3M Corporation, or wire grid polarisers such as ProFlux™ fromMoxtek. Reflective linear polarisers may further comprise cholestericreflective materials and a quarter-wave plate arranged in series.

A retarder arranged between a linear polariser and a parallel linearanalysing polariser that introduces no relative net phase shift providesfull transmission of the light other than residual absorption within thelinear polariser.

A retarder that provides a relative net phase shift between orthogonalpolarisation components changes the SOP and provides attenuation at theanalysing polariser.

In the present disclosure an ‘A-plate’ refers to an optical retarderutilizing a layer of birefringent material with its optical axisparallel to the plane of the layer.

A ‘positive A-plate’ refers to positively birefringent A-plates, i.e.A-plates with a positive Δn.

In the present disclosure a ‘C-plate’ refers to an optical retarderutilizing a layer of birefringent material with its optical axisperpendicular to the plane of the layer. A ‘positive C-plate’ refers toa positively birefringent C-plate, i.e. a C-plate with a positive Δn. A‘negative C-plate’ refers to a negatively birefringent C-plate, i.e. aC-plate with a negative Δn.

‘O-plate’ refers to an optical retarder utilizing a layer ofbirefringent material with its optical axis having a component parallelto the plane of the layer and a component perpendicular to the plane ofthe layer. A ‘positive O-plate’ refers to positively birefringentO-plates, i.e. O-plates with a positive Δn.

Achromatic retarders may be provided wherein the material of theretarder is provided with a retardance Δn. d that varies with wavelengthλ asΔn.d/λ=κ  eqn. 3where κ is substantially a constant.

Examples of suitable materials include modified polycarbonates fromTeijin Films. Achromatic retarders may be provided in the presentembodiments to advantageously minimise color changes between polarangular viewing directions which have low luminance reduction and polarangular viewing directions which have increased luminance reductions aswill be described below.

Various other terms used in the present disclosure related to retardersand to liquid crystals will now be described.

A liquid crystal cell has a retardance given by Δn. d where Δn is thebirefringence of the liquid crystal material in the liquid crystal celland d is the thickness of the liquid crystal cell, independent of thealignment of the liquid crystal material in the liquid crystal cell.

Homogeneous alignment refers to the alignment of liquid crystals inswitchable liquid crystal displays where molecules align substantiallyparallel to a substrate. Homogeneous alignment is sometimes referred toas planar alignment. Homogeneous alignment may typically be providedwith a small pre-tilt such as 2 degrees, so that the molecules at thesurfaces of the alignment layers of the liquid crystal cell are slightlyinclined as will be described below. Pretilt is arranged to minimisedegeneracies in switching of cells.

In the present disclosure, homeotropic alignment is the state in whichrod-like liquid crystalline molecules align substantiallyperpendicularly to the substrate. In discotic liquid crystalshomeotropic alignment is defined as the state in which an axis of thecolumn structure, which is formed by disc-like liquid crystallinemolecules, aligns perpendicularly to a surface. In homeotropicalignment, pretilt is the tilt angle of the molecules that are close tothe alignment layer and is typically close to 90 degrees and for examplemay be 88 degrees.

In a twisted liquid crystal layer a twisted configuration (also known asa helical structure or helix) of nematic liquid crystal molecules isprovided. The twist may be achieved by means of a non-parallel alignmentof alignment layers. Further, cholesteric dopants may be added to theliquid crystal material to break degeneracy of the twist direction(clockwise or anti-clockwise) and to further control the pitch of thetwist in the relaxed (typically undriven) state. A super twisted liquidcrystal layer has a twist of greater than 180 degrees. A twisted nematiclayer used in spatial light modulators typically has a twist of 90degrees.

Liquid crystal molecules with positive dielectric anisotropy areswitched from a homogeneous alignment (such as an A-plate retarderorientation) to a homeotropic alignment (such as a C-plate or O-plateretarder orientation) by means of an applied electric field.

Liquid crystal molecules with negative dielectric anisotropy areswitched from a homeotropic alignment (such as a C-plate or O-plateretarder orientation) to a homogeneous alignment (such as an A-plateretarder orientation) by means of an applied electric field.

Rod-like molecules have a positive birefringence so that n_(e)>n_(o) asdescribed in eqn. 2. Discotic molecules have negative birefringence sothat n_(e)<n_(o).

Positive retarders such as A-plates, positive O-plates and positiveC-plates may typically be provided by stretched films or rod-like liquidcrystal molecules. Negative retarders such as negative C-plates may beprovided by stretched films or discotic like liquid crystal molecules.

Parallel liquid crystal cell alignment refers to the alignment directionof homogeneous alignment layers being parallel or more typicallyantiparallel. In the case of pre-tilted homeotropic alignment, thealignment layers may have components that are substantially parallel orantiparallel. Hybrid aligned liquid crystal cells may have onehomogeneous alignment layer and one homeotropic alignment layer. Twistedliquid crystal cells may be provided by alignment layers that do nothave parallel alignment, for example oriented at 90 degrees to eachother.

Transmissive spatial light modulators may further comprise retardersbetween the input display polariser and the output display polariser forexample as disclosed in U.S. Pat. No. 8,237,876, which is hereinincorporated by reference in its entirety. Such retarders (not shown)are in a different place to the passive retarders of the presentembodiments. Such retarders compensate for contrast degradations foroff-axis viewing locations, which is a different effect to the luminancereduction for off-axis viewing positions of the present embodiments.

Terms related to privacy display appearance will now be described.

A private mode of operation of a display is one in which an observersees a low contrast sensitivity such that an image is not clearlyvisible. Contrast sensitivity is a measure of the ability to discernbetween luminances of different levels in a static image. Inversecontrast sensitivity may be used as a measure of visual security, inthat a high visual security level (VSL) corresponds to low imagevisibility.

For a privacy display providing an image to an observer, visual securitymay be given as:VSL=(Y+R)/(Y−K)  eqn.4

where VSL is the visual security level, Y is the luminance of the whitestate of the display at a snooper viewing angle, K is the luminance ofthe black state of the display at the snooper viewing angle and R is theluminance of reflected light from the display.

Panel Contrast Ratio is Given as:C=Y/K  eqn. 5

For high contrast optical LCD modes, the white state transmissionremains substantially constant with viewing angle. In the contrastreducing liquid crystal modes of the present embodiments, white statetransmission typically reduces as black state transmission increasessuch thatY+K˜P.L  eqn. 6

The visual security level may then be further given as:

$\begin{matrix}{{VSL} = \frac{\left( {C + {{I.\rho}/{\pi.\left( {C + 1} \right)}/\left( {P.L} \right)}} \right)}{\left( {C - 1} \right)}} & {{eqn}.7}\end{matrix}$

where off-axis relative luminance, P is typically defined as thepercentage of head-on luminance, L at the snooper angle and the displaymay have image contrast ratio C and the surface reflectivity is ρ.

The off-axis relative luminance, P is sometimes referred to as theprivacy level. However, such privacy level P describes relativeluminance of a display at a given polar angle compared to head-onluminance, and is not a measure of privacy appearance.

The display may be illuminated by Lambertian ambient illuminance I. Thusin a perfectly dark environment, a high contrast display has VSL ofapproximately 1.0. As ambient illuminance increases, the perceived imagecontrast degrades, VSL increases and a private image is perceived.

For typical liquid crystal displays the panel contrast C is above 100:1for almost all viewing angles, allowing the visual security level to beapproximated to:VSL=1+I.ρ/(π.P.L)  eqn. 8

The perceptual image security may be determined from the logarithmicresponse of the eye, such thatS=log₁₀(V)  eqn. 9

Desirable limits for S were determined in the following manner. In afirst step a privacy display device was provided. Measurements of thevariation of privacy level, P(θ) of the display device with polarviewing angle and variation of reflectivity ρ(θ) of the display devicewith polar viewing angle were made using photopic measurement equipment.A light source such as a substantially uniform luminance light box wasarranged to provide illumination from an illuminated region that wasarranged to illuminate the privacy display device along an incidentdirection for reflection to a viewer positions at a polar angle ofgreater than 0° to the normal to the display device. The variation I(θ)of illuminance of a substantially Lambertian emitting lightbox withpolar viewing angle was determined by measuring the variation ofrecorded reflective luminance with polar viewing angle taking intoaccount the variation of reflectivity ρ(θ). The measurements of P(θ),r(θ) and I(θ) were used to determine the variation of Security FactorS(θ) with polar viewing angle along the zero elevation axis.

In a second step a series of high contrast images were provided on theprivacy display including (i) small text images with maximum font height3 mm, (ii) large text images with maximum font height 30 mm and (iii)moving images.

In a third step each observer (with eyesight correction for viewing at1000 mm where appropriate) viewed each of the images from a distance of1000 m, and adjusted their polar angle of viewing at zero elevationuntil image invisibility was achieved for one eye from a position nearon the display at or close to the centre-line of the display. The polarlocation of the observer's eye was recorded. From the relationship S(θ),the security factor at said polar location was determined. Themeasurement was repeated for the different images, for various displayluminance Y_(max), different lightbox illuminance I(q=0), for differentbackground lighting conditions and for different observers.

From the above measurements S<1.0 provides low or no visual security,1.0≤S<1.5 provides visual security that is dependent on the contrast,spatial frequency and temporal frequency of image content, 1.5≤S≤1.8provides acceptable image invisibility (that is no image contrast isobservable) for most images and most observers and S≥1.8 provides fullimage invisibility, independent of image content for all observers.

In comparison to privacy displays, desirably wide-angle displays areeasily observed in standard ambient illuminance conditions. One measureof image visibility is given by the contrast sensitivity such as theMichelson contrast which is given by:M=(I _(max) −I _(min))/(I _(max) +I _(min))  eqn. 10

and so:M=((Y+R)−(K+R))/((Y+R)+(K+R))=(Y−K)/(Y+K+2.R)  eqn. 11

Thus the visual security level (VSL), is equivalent (but not identicalto) 1/M. In the present discussion, for a given off-axis relativeluminance, P the wide-angle image visibility, W is approximated asW=1/VSL=1/(1+I.p/(π.P.L))  eqn. 12

In the present discussion the colour variation Δε of an output colour(u_(w)′+Δu′,v_(w)′+Δv′) from a desirable white point (u_(w)′, v_(w)′)may be determined by the CIELUV colour difference metric, assuming atypical display spectral illuminant and is given by:Δε=(Δu′ ² +Δv′ ²)^(1/2)  eqn. 13

Catadioptric elements employ both refraction and reflection, which maybe total internal reflection or reflection from metallised surfaces.

The structure and operation of various directional display devices willnow be described. In this description, common elements have commonreference numerals. It is noted that the disclosure relating to anyelement applies to each device in which the same or correspondingelement is provided. Accordingly, for brevity such disclosure is notrepeated.

It would be desirable to provide a switchable privacy display usingemissive spatial light modulators.

FIG. 1A is a schematic diagram illustrating in side perspective view aswitchable privacy display 100 for use in ambient illumination 604comprising an OLED emissive spatial light modulator 48, parallax barrier700, output polariser 218 and reflection control quarter-wave retarder228, reflective polariser 302, a switchable polar control retarder 300and an additional polariser 318 arranged on the output side of thespatial light modulator 48; and FIG. 1B is a schematic diagramillustrating in front view alignment of optical layers in the opticalstack of FIG. 1A.

Emissive spatial light modulator 48 comprises an array of red, green andblue pixels 220, 222, 224 arranged in a pixel layer 214 on backplanesubstrate 212. The pixels are arranged to output light 400 along anoutput direction. The pixels 220, 222, 224 comprise light emittingdiodes that are organic light emitting diodes comprising an organiclight emitting material 232.

The regions 226 between the pixels 220, 222, 224 comprises controlelectronics and are typically reflective for OLED pixel layers 214.

Parallax barrier 700 comprises an array of apertures 702 with alightabsorbing region 704 between the apertures. The parallax barrier 700 isarranged a two dimensional array of apertures 702, each pixel 220, 222,224 being aligned with a respective aperture.

The parallax barrier 700 is arranged on a spacer layer 216 that providesa separation from the pixel layer 214 with a parallax distance d alongan axis 199 along a normal to the plane of the pixel layer 214.

An output polariser 218 is arranged on the output of the spatial lightmodulator 48, the output polariser 218 being a linear polariser with anelectric vector transmission direction 219. A reflection controlquarter-wave retarder 228 with optical axis direction 229 is arrangedbetween the output polariser 218 and spatial light modulator 48. Theretarder 228 may be provided by a stretched birefringent film such aspolycarbonate. Advantageously low cost retarders 228 may be provided.

In the embodiment of FIGS. 1A-B the parallax barrier 700 is arrangedbetween the pixel layer 214 and the reflection control quarter-waveretarder 228. In other embodiments (not shown) the quarter-wave retarder228 may be provided by a layer formed between the pixel layer 214 andthe parallax barrier 700. Such retarders 228 may comprise cured reactivemesogen liquid crystal layers for example. Advantageously a retarder maybe provided with thickness that is the same or less than the desirablethickness d as will be described further below.

Additional polariser 318 is arranged on the output side of the outputpolariser 218, the additional polariser 318 being a linear polariser.Polar control retarder 300 is arranged between the output polariser 218and the additional polariser 318. The output polariser 218 and theadditional polariser 318 are arranged to pass respective linearlypolarised polarisation states.

The polar control retarder 300 comprises passive retarders 330A, 330Band switchable liquid crystal retarder 301 that comprises transparentsubstrates 312, 316 and switchable liquid crystal layer 314. Voltagedriver 350 may be used to select mode of operation, and may becontrolled by controller 352.

Illustrative embodiments are described with respect to FIG. 9 , FIG.17D, FIGS. 22A-B and FIG. 23A as will be described in further detailbelow.

The embodiment of FIG. 1A further comprises a reflective polariser 302arranged between the output polariser 218 and the at least one polarcontrol retarder 300, the reflective polariser 302 being a linearpolariser with electric vector transmission direction 303 arranged topass the same linearly polarised polarisation state as the outputpolariser 218.

The structure and operation of polar control retarders 300 andreflective polariser 302 are described in further detail in U.S. PatentPubl. No. 2019-0086706, in U.S. Patent Publ. No. 2019-0250458, in U.S.Patent Publ. No. 2018-0321553, in U.S. Patent Publ. No. 2020-0159055,and in WIPO Publ. No. WO 2018/208618, all of which are hereinincorporated by reference in their entireties. The polar controlretarders in the present description can be replaced by any of the onesdescribed therein.

The operation of the switchable liquid crystal retarder will bedescribed further with reference to FIGS. 10A-D below. In the privacymode of operation, the at least one polar control retarder 300 iscapable of simultaneously introducing no net relative phase shift toorthogonal polarisation components of light passed by the outputpolariser 218 along an axis 199 along a normal to the plane of the atleast one polar control retarder 300 and introducing a relative phaseshift to orthogonal polarisation components of light passed by thereflective polariser 302 along an axis 197 inclined to a normal to theplane of the at least one polar control retarder 300. In the public modeof operation, the at least one polar control retarder 300 is capable ofsimultaneously introducing no net relative phase shift to orthogonalpolarisation components of light passed by the output polariser 218along an axis 199 along a normal to the plane of the at least one polarcontrol retarder 300 and introducing substantially no relative phaseshift to orthogonal polarisation components of light passed by thereflective polariser 302 along an axis 197 inclined to a normal to theplane of the at least one polar control retarder 300.

Such phase control of output light when combined with the reflectivepolariser 302 advantageously achieves reduction of off-axis luminanceand increase of off-axis reflectivity of the display of FIG. 1A inprivacy mode. In public mode, high transmission and low displayreflectivity is achieved over a wide range of polar angles. Further inboth modes of operation high transmission and low reflectivity isachieved for on-axis display users. Advantageously a display user sees ahigh luminance and high contrast image in both modes while an off-axissnooper sees a high visual security level in privacy mode and anoff-axis user sees high image visibility in public mode.

The structure and operation of the parallax barrier 700 will now bedescribed.

In emissive displays, high luminance is typically provided at high polarangles. A typical emissive display such as an OLED display may forexample provide luminance of greater than 25% of head-on luminance at apolar angle of 60 degrees. Micro-LED displays that comprise inorganicLEDs may have substantially Lambertian luminance output so luminance at60 degrees may approach 100% of head-on luminance.

As will be described in FIGS. 11A-B, the polar control retarders 300 aretypically arranged to provide optimum visual security level at a designpolar location. Such polar location may for example be +/−45 degreeslateral angle and 0 degrees elevation. At lateral angles that aredifferent to the design polar location 5 degrees, the reduction ofluminance and increase of reflectivity are reduced.

It would be desirable to provide a switchable privacy display with highvisual security in privacy mode at polar angles greater than 45 degreesand with high image visibility in public mode at polar angles greaterthan 45 degrees. Desirably off-axis luminance may be at least 2.5% andpreferably at least 5% of head-on luminance for high image visibility intypical ambient lighting conditions. Desirably off-axis luminance may beless than 1% and preferably less than 0.5% for high image security intypical ambient lighting conditions. It would be further desirable toprovide low chromatic variations with polar viewing angle.

FIGS. 2A-B are schematic diagrams illustrating in side views a parallaxbarrier 700 for the privacy display 100 of FIGS. 1A-B. FIGS. 2A-Billustrate a cross section in the direction θ in which the apertures 702are closest.

Features of the arrangements of FIGS. 2A-2B not discussed in furtherdetail may be assumed to correspond to the features with equivalentreference numerals as discussed above, including any potentialvariations in the features.

Various output layers such as polarisers and retarders that are arrangedat the output of the parallax barrier are indicated by monolithic layer110 for purposes of description.

Desirable ranges for the structure of the parallax barrier have beenestablished by means of simulation of retarder stacks, parallaxbarriers, pixel arrangements and experiments with display opticalstacks.

Light rays 710 that are directed along the axis 199 that is normal tothe spatial light modulator 48 are directed through the respectivealigned aperture 702 of width a. The aperture size a is larger than thepixel width w to achieve 100% luminance for head-on directions. Thusalong the direction in which the apertures 702 are closest, theapertures 702 have a width a and the pixels 220, 222, 224 have a width wmeeting the requirement that:a≥w  eqn.14

Some light rays 726 are directed in off-axis directions such that theluminance in said off-axis direction is reduced in comparison to thehead-on luminance for rays 710. The minimum absorption provided by theparallax barrier is desirably 50% so that along the direction in whichthe apertures 702 are closest, the apertures 702 have a width a, thepixels 220, 222, 224 have a pitch p and the pixels 220, 222, 224 have awidth w meeting the requirement that:a≤(p−w/2)  eqn. 15

Some light rays 712 from pixels 220, 222, 224 are incident on the lowerside of the parallax barrier absorbing regions 704 and may be absorbed.The angle for minimum transmission is provided when the light ray 712from the centre of the pixel is incident on the centre of the absorbingregion 704. The polar angle in air ϕmin may be at least 45 degrees sothat along the direction in which the apertures 702 are closest andmaterial between the parallax barrier 700 and the pixels 220, 222, 224has a refractive index n meeting the requirement that:d≤p√(2n ²−1)/2  eqn. 16

Light rays 716 from the centre of pixels 220, 222, 224 that are incidenton the edge of the parallax barrier 700 absorbing region are at thepolar angle in air #max at which the luminance is at most 50% of thehead-on luminance. Desirably #max (in air) is at most 90 degrees andthus the parallax barrier has a separation d from the pixels 220, 222,224 meeting the requirement that:d≥a√(n ²−1)/2  eqn. 17

In other embodiments the desirable angle for #max is preferably at most60 degrees and thus the parallax barrier has a separation d from thepixels 220, 222, 224 meeting the requirement that:d≥an√(1−3/(4n ²))/√3  eqn. 18

Illustrative dimensions in micrometers for a pixel pitch of 50micrometers in the direction in which the pixels are closest andrefractive index of the medium between the pixel layer 214 and parallaxbarrier 700 of 1.5 are given in TABLE 1.

TABLE 1 Pixel Pixel Aperture, a Thickness, d pitch, p width, w MinimumMaximum Minimum Maximum 50 μm 25 μm 25 μm 37.5 μm 28.0 μm 46.8 μm 50 μm 3 μm  3 μm 48.5 μm 28.0 μm 46.8 μm

Thus the thickness, d of the parallax barrier spacer layer 216 is of theorder of 30 m. Such thickness is typical of typical encapsulation layersfor OLED panels as will be described further below. Parallax barrier 700may be formed in desirable proximity to pixel layer 214 toadvantageously achieve desirable performance for a switchable privacydisplay.

By way of comparison with the present embodiments, TABLE 2 illustrates astructure for a two view parallax barrier autostereoscopic display forthe same pixel pitch and pixel widths wherein the pixel columns aredirected to viewing windows, each window providing a left- or right-eyeimage. The ranges of desirable thickness are provided for minimum windowsize of 60 mm, maximum window size 67 mm, minimum viewing distance 250mm and maximum window distance 700 mm.

TABLE 2 Pixel Pixel Aperture, a Thickness, d pitch, p width, w MinimumMaximum Minimum Maximum 50 μm 25 μm  ~5 μm 25 μm 290 μm 875 μm 50 μm  3μm ~10 μm 25 μm 290 μm 875 μm

Advantageously the present embodiments achieve increased luminance andlower thickness than that used for autostereoscopic display.Autostereoscopic display parallax barriers do not achieve desirableprivacy display luminance control characteristics.

Some light rays 714 may pass through apertures 702 at angles greaterthan the critical angle and are thus totally internally reflected. Suchrays may be absorbed by the top of the parallax barrier absorbingregions 704. Other absorption mechanisms will be discussed furtherbelow.

The absorbing regions 704 may be partially absorbing. Some light rays712 may pass through the absorbing regions 704 due to reduced absorptionof the absorbing material. Additionally or alternatively the absorbingregions 704 may be arranged with sub-apertures 722 arranged to permitpropagation of light rays 712. The sub-apertures 722 may have size anddensity arranged to provide desirable illumination profile in publicmode of operation.

In an illustrative example, the barrier regions 704 may transmit 5% ofincident light rays by means of sub-apertures 722. For a Lambertianemitting pixel 220, 222, 224, the luminance at an angle of 60 degreesmay be arranged to be 5% by means of control of density and size ofsub-apertures 722 and width of aperture for a given pixel pitch p andpixel size a. In privacy mode, the luminance may be less than 1%.Advantageously image visibility in public mode of operation may beincreased while high visual security level may be achieved in privacymode by means of the polar control retarders 300.

Arrangements of parallax barrier pitch p′ compared to pixel pitch p willnow be described.

FIG. 3A is a schematic diagram illustrating in side perspective view thealignment of the parallax barrier 700 with the pixels 220, 222, 224 ofFIG. 1A for a non-pupillated output.

The parallax barrier 700 directs light from each pixel 220, 222, 224into a common viewing window 26. In FIG. 3A, the common viewing windowsare angularly aligned, in other words the common sub-windows 26 fromeach pixel and aligned barrier aperture 702 overlap at infinity and arecollimated. The window represents the angular distribution of light fromeach slit. Advantageously, such an arrangement provides similar spatialroll-off across the area of the display 100 as the polar controlretarders 300 and polarisers 218, 318. Natural variations of imageuniformity across the display area are achieved for a moving observer,that is the part of the display nearest to the user appears thebrightest.

FIG. 3B is a schematic diagram illustrating in side perspective view thealignment of the parallax barrier 700 with the pixels 220, 222, 224 ofFIG. 1A for a pupillated output. The pitch p′ along the direction inwhich the apertures 702 are closest is smaller than the pitch p of therespective aligned pixels 220, 222, 224 along the direction in which thepixels 220, 222, 224 are closest. In any given direction the pitch s′ ofthe apertures 702 are closest is smaller than the pitch s of therespective aligned pixels 220, 222, 224.

The viewing window 26 is formed at a viewing window plane at distance vthat is on the output side of the spatial light modulator 48 such thatthe common viewing window at which the viewing windows overlap is at afinite distance. Advantageously for a head-on observer located at thewindow plane the luminance uniformity across the area of the display isincreased.

At least some of the apertures of the parallax barrier may comprise acolour filter 703R, 703G, 703B so the apertures of the parallax barriercomprise an array of red, green and blue colour filters. The colourfilters may correspond to the colour of the respective aligned pixels220, 222, 224. The filters reduce the colour crosstalk from for exampleblue light leaking into the red pixel aperture advantageously achievingincreased colour gamut.

Alternatively only some of the apertures 702 may comprise a colourfilter for example the apertures 702 corresponding to the red and greenemitting pixels 220, 222 may comprise a yellow transmission filter. Insome embodiments coloured emission may be achieved by for example blueemitting pixels and colour conversion materials aligned to the pixels220, 222 to achieve coloured output. The yellow colour filters of theapertures 702 may provide absorption of residual blue light,advantageously achieving increased colour gamut.

The materials of the colour filter of the aperture 702 may comprise anon-scattering or low scattering material so that the angular controlfunction of the apertures 702 and absorbing regions 704 is maintained.

Features of the arrangements of FIGS. 3A-B not discussed in furtherdetail may be assumed to correspond to the features with equivalentreference numerals as discussed above, including any potentialvariations in the features.

FIG. 4 is a schematic diagram illustrating in top view an arrangement ofuniform emissive pixels 220, 222, 224 and eye spot locations 260, 262,264 for various polar viewing angles.

The pixels 220, 222, 224 are arranged in columns and rows, the directionin which the apertures 702 are closest is at 45 degrees with respect tothe electric vector transmission direction 219 of the output linearpolariser; and each pixel 220, 222, 224 has a light emission region thatis a square shape with edges rotated by 45 degrees with respect to theelectric vector transmission direction of the output linear polariser.

The apertures 702 have a square shape with edges rotated by 45 degreeswith respect to the electric vector transmission direction of the outputlinear polariser.

The eye spot locations 260, 262, 264 represent the image of anobserver's pupil at the pixel layer 214 provided by the aperture 702.The eye spot location 260 represents the location of a head-onobserver's pupil. As the spot location 260 has a size larger than thepixel, the observer sees the same brightness as the pixel brightness and100% luminance is achieved.

For location 262, the observer's eye is located in a display quadrant(with non-zero lateral angle and elevation) and at a transmissionminimum. For location 262, the observer's eye is located with zeroelevation with a lateral offset and at a transmission minimum.

The eye spot location 264 has a greater separation from the on-axislocation than location 262 so that the transmission minimum is nearestin the quadrant rather than the lateral direction. Advantageouslysuppression in viewing quadrants can be optimised.

Further the pixel arrangement of FIG. 4 achieves desirable rendering ofhorizontal and vertical lines while reducing the number of red and bluepixels compared to the number of green pixels.

OLED displays typically provide different emitting areas for red, greenand blue pixels due to the different luminous emittance (lumen/mm²) forthe respective material systems. By way of comparison in the embodimentof FIG. 4 the pixels 220, 222, 224 of the present disclosure when usedwith two dimensional aperture 702 arrays comprise emitting regions withsubstantially the same area for all pixels. Advantageously the variationof white point with viewing angle may be minimised.

It would be desirable to compensate for the different luminous emittanceof red, green and blue emitters in an OLED display to achieve adesirable white point.

The luminous emittance of each pixel 220, 222, 224 may be varied byadjusting the drive current between the different coloured pixels sothat white point is maintained. Thus the green pixels 222 may have forexample twice the emitting area than conventionally used. The drivecurrent for the green pixels 222 and red pixels 220 may be reduced toachieve desirable white points.

It may be desirable to provide drive currents that are the same as usedfor typical OLED displays.

FIG. 5 is a schematic diagram illustrating in top view an arrangement ofstructured emissive pixels 220, 222, 224 and eye spot locations forvarious polar viewing angles.

For at least some of the pixels 220, 222, 224 the light emission regionof at least some of the pixels comprises light emitting sub-regions232R, 232G, 232B and non-light emitting sub-regions 234. The ratio ofthe area of light emitting sub-regions to non-light emitting regions isdifferent for red, green and blue pixels 220, 222, 224. The sub-regions232R, 232G, 232B may be provided within the same area for each of thepixels. The distribution of sub-regions 232 and eye-spot 260 size may bearranged to provide substantially uniform roll-off of luminance withpolar angle to advantageously achieve minimised variation of white pointwith viewing angle; and desirable drive currents may be provided foreach of the colour pixels 220, 222, 224.

Features of the arrangements of FIGS. 4-5 not discussed in furtherdetail may be assumed to correspond to the features with equivalentreference numerals as discussed above, including any potentialvariations in the features.

The structure of OLED displays comprising the parallax barrier 700 willnow be described.

FIG. 6 is a schematic diagram illustrating in side view the structure ofa spatial light modulator 48 and aligned parallax barrier 700 comprisingupper ingress reduction layers 750, 752.

Pixel layer 214 is formed on the substrate 212 and comprises thin filmcontrol circuitry 240 that comprises thin film transistors, capacitors,electrodes and other electronic control components. Electrical vias 242provide connection to electrode 230 that is typically reflective.Emission layers 232R, 232G, 232B are arranged between electron transportlayers 236R, 232G, 232B and hole transport layers 238R, 238G, 238B.Transparent electrode 244 is arranged to provide output side electricalconnection.

The emission layer thickness 233R, 233G, 233B and electron transferlayer thickness 237R, 237G, 237B may be adjusted to provide suitablelight output characteristics. The thickness 233R, 233G, 233B of thelight emitting material is different for each of the red, green and bluelight emitting regions in pixels 220, 222, 224.

In another arrangement (not shown) hole and electron transport layers236, 238 may be alternatively arranged below and above emission region232. The total thickness of pixel layer 214 may typically be one micronor less, and so differences in location of emission layer 232 are smallin comparison to the distance of the spacer layer 216.

The display 100 device has one or more additional layers 750, 752arranged in the spacer layer 216 between the pixel layer 214 and theparallax barrier 700, wherein the pixels 220, 222, 224, the one or moreadditional layers and the parallax barrier 700 are formed as amonolithic stack. The one or more additional layers comprise at leastone light transmitting inorganic layer 752 arranged to provide a barrierto water and oxygen. The material 752 may for example be an oxidematerial such as SiO_(x).

The layers 750 may be provided with an organic material. The substrate212 may be further provided with layers 750, 752 (not shown). Ingress towater and oxygen may be inhibited while maintaining a flexible displaystructure with desirable mechanical properties. Advantageously displaylifetime may be increased.

The total thickness d may be adjusted to advantageously achieve thedesirable luminance roll-off as described elsewhere herein.

The parallax barrier 700 further comprises at least one lighttransmitting inorganic material that is arranged to provide a barrier towater and oxygen. Advantageously increased lifetime may be provided.Further non-transmissive barrier layers may be provided in theabsorption regions 704 to achieve increased inhibition to ingress overat least part of the barrier.

Further reduction of ingress may be desirable. The parallax barrier 700is arranged between the pixel layer 214 and at least one lighttransmitting inorganic layer 752 that is arranged to provide a barrierto water and oxygen. The inorganic layers 752 are separated by organiclayer 750. Advantageously high resistance to water and oxygen ingressmay be provided in a flexible substrate.

FIG. 7 is a schematic diagram illustrating in side view the structure ofa spatial light modulator 48 and aligned parallax barrier comprising aglass material 110. In comparison to the arrangement of FIG. 6 a glassmaterial 110 may be provided for the cover layer 217 that provides highbarrier layer resistance to oxygen and water ingress in comparison tothe layers 752, 750 of FIG. 6 . The spacer layer 216 may be provided byan adhesive material or a polymer material. Alternatively the spacerlayer 216 may be provided by a glass material which is thinned bychemical-mechanical polishing after fabrication of the backplane 212 andpixel layer 214 to achieve the desirable thickness d.

Features of the arrangements of FIGS. 6A-B not discussed in furtherdetail may be assumed to correspond to the features with equivalentreference numerals as discussed above, including any potentialvariations in the features.

Arrangements of transmission profile of the parallax barrier 700 willnow be described in further detail.

FIGS. 8A-C are schematic graphs illustrating the variation of parallaxbarrier 700 transmission with position for various parallax barrier 700structures.

FIG. 8A illustrates a first transmission profile 701 of relativetransmission against position in a direction θ at which the aperturesare closest; wherein the absorption regions 704 have 100% absorption.Advantageously very low luminance can be achieved in privacy mode atpolar angles greater than 45 degrees.

FIG. 8B illustrates increased transmission 705 for absorption regions704, for example by control of the thickness of the material used toform the absorption regions 704. The absorption of the region of theparallax barrier 700 between the apertures 702 is less than 100%, and isgreater than 80% preferably greater than 90% and more preferably greaterthan 95%. Transmission 705 may for example be less than 5% or less than2.5%. Advantageously increased luminance may be provided at higher polarviewing angles in public mode of operation.

FIG. 8C illustrates increased transmission for absorption regions 704 bymeans of sub-aperture regions 722 as illustrated in FIG. 2A for example.Average transmission 705 across the light absorbing regions 704 may forexample be less than 5% or less than 2.5%. Advantageously increasedluminance may be provided at higher polar viewing angles in public modeof operation.

The structure of an illustrative embodiment of the polar retarder ofFIG. 1A will now be described.

Features of the arrangements of FIGS. 8A-C not discussed in furtherdetail may be assumed to correspond to the features with equivalentreference numerals as discussed above, including any potentialvariations in the features.

In the embodiment of FIGS. 1A-B, the polar control retarder 300comprises passive polar control retarder 330 and switchable liquidcrystal retarder 301, but in general may be replaced by otherconfigurations of at least one retarder, some examples of which arepresent in the devices described below.

FIG. 9 is a diagram illustrating in perspective side view an arrangementof a switchable polar control retarder 300 comprising a liquid crystalretarder 301 comprising a switchable liquid crystal layer 314 withhomogeneous alignment and crossed A-plate polar control retarders 330A,330B. Features of the arrangements of FIG. 9 not discussed in furtherdetail may be assumed to correspond to the features with equivalentreference numerals as discussed above, including any potentialvariations in the features.

An illustrative embodiment is given in TABLE 3 and polar profiles inprivacy and public mode.

TABLE 3 Passive polar control retarder(s) Active LC retarder Δn.d/Alignment Pretilt/ Δn.d/ Voltage/ Mode Type nm layers deg nm Δε V PublicCrossed A +500 @ 45°  Homogeneous 2 750 13.2 10 Privacy +500 @ 135°Homogeneous 2 2.3

The switchable liquid crystal retarder 301 comprises two surfacealignment layers 419 a, 419 b disposed adjacent to the layer of liquidcrystal material 421 and on opposite sides thereof and each arranged toprovide homogeneous alignment in the adjacent liquid crystal material421. The layer 314 of liquid crystal material 421 of the switchableliquid crystal retarder 301 comprises a liquid crystal material 421 witha positive dielectric anisotropy.

The passive polar control retarder 330 is provided by a pair of A-plates330A, 330B that have crossed axes. In the present embodiments, ‘crossed’refers to an angle of substantially 90° between the optical axes of thetwo retarders in the plane of the retarders. To reduce cost of retardermaterials, it is desirable to provide materials with some variation ofretarder orientation due to stretching errors during film manufacturefor example. Variations in retarder orientation away from preferabledirections can reduce the head-on luminance and increase the minimumtransmission. Preferably the angle 310A is at least 35° and at most 55°,more preferably at least 40° and at most 50° and most preferably atleast 42.5° and at most 47.5°. Preferably the angle 310B is at least125° and at most 145°, more preferably at least 130° and at most 135°and most preferably at least 132.5° and at most 137.5°.

Homogeneous alignment advantageously provides reduced recovery timeduring mechanical distortion, such as when touching the display. Thepassive retarders 330A, 330B may be provided using stretched films toadvantageously achieve low cost and high uniformity. Further field ofview for liquid crystal retarders with homogeneous alignment isincreased while providing resilience to the visibility of flow of liquidcrystal material during applied pressure.

The at least one polar control retarder 300 is arranged, in a firstswitchable state of the switchable liquid crystal retarder 301,simultaneously to introduce no net relative phase shift to orthogonalpolarisation components of light passed by the reflective polariser 302along an axis 199 along a normal to the plane of the at least one polarcontrol retarder 300 and to introduce a net relative phase shift toorthogonal polarisation components of light passed by the reflectivepolariser 302 along an axis 197 inclined to a normal to the plane of theat least one polar control retarder 300; and in a second switchablestate of the switchable liquid crystal retarder 301, simultaneously tointroduce no net relative phase shift to orthogonal polarisationcomponents of light passed by the reflective polariser 302 along an axis199 along a normal to the plane of the at least one polar controlretarder 300 and to introduce no net relative phase shift to orthogonalpolarisation components of light passed by the reflective polariser 302along an axis 197 inclined to a normal to the plane of the at least onepolar control retarder 300.

Such phase shifts provide polar transmission and reflectivity profilesthat achieve (i) high transmission and low reflectivity on-axis; (ii) ina privacy mode reduced transmission and increased reflectivity off-axis;and (ii) in a public mode high transmission and low reflectivityoff-axis. Advantageously a switchable privacy display provides highimage quality to a head-on user, high visual security level to off-axissnooper and high image visibility to off-axis display users as will nowbe described.

FIG. 10A is a schematic diagram illustrating in side view propagation ofoutput light from a spatial light modulator 48 through the optical stackof FIG. 1A in a public mode of operation.

In the public mode of operation, light rays 710 emitted by the pixels220, 222, 224 and transmitted through the barrier 700 aperture 702 in anon-axis direction have a polarisation state 360 parallel to the electricvector transmission direction 219 of the output polariser 218. Theon-axis ray 710 then traverses the multiple retarder layers 300comprising the switchable liquid crystal retarder 301 and the passiveretarder 330. In public mode, the switchable liquid crystal retarder 301is in the off state with a different control voltage across the liquidcrystal layer 314.

The polarised state of the on-axis light ray 710 therefore experiences aretardation when passing through the switchable liquid crystal retarder301. In the case where the passive retarder 330 is a C-plate retarder,the on-axis light ray 710 is propagating in a direction that issubstantially parallel to the optical axis of the passive retarder 330.The on-axis light ray 710 therefore experiences minimal retardation whenpassing through the passive retarder 330. The combined effect off theplurality of retarders 300 results in the on-axis light ray 710 exitingthe plurality of retarders 300 with the same or similar linearpolarisation state 362 to the linear polarisation state 360 with whichthe on-axis light ray 710 entered the plurality of retarders 300. Thislinear polarisation state 362 is parallel to the electric vectortransmission direction 319 of the additional polariser 318 and theon-axis ray 710 therefore exits the display device 100 with a relativelyunmodified luminance.

In the public mode, the off-axis ray 726 that is transmitted by thebarrier 700 aperture 702 traverses the plurality of retarders 300 in asimilar fashion to the on-axis ray 710. Thus, when the switchable liquidcrystal retarder 301 is in a first state of said two states, theplurality of retarders 300 provides no overall transformation ofpolarisation states 360, 361 of light ray 710 passing therethroughperpendicular to the plane of the switchable retarder or light ray 726passing therethrough at an acute angle to the perpendicular to the planeof the switchable retarder 301.

Polarisation state 362 is substantially the same as polarisation state360 and polarisation state 364 is substantially the same as polarisationstate 361. Thus the angular transmission profile is substantiallyuniformly transmitting across a wide polar region.

In other words, when the layer 314 of liquid crystal material 414 is inthe first state of said two states, the plural retarders 300 provide nooverall retardance to light passing therethrough perpendicular to theplane of the retarders or at an acute angle to the perpendicular to theplane of the plural retarders 300.

Advantageously the variation of display luminance with viewing angle inthe first state is substantially unmodified. Multiple users mayconveniently view the display from a wide range of viewing angles.

FIG. 10B is a schematic diagram illustrating in side view propagation oflight rays from an ambient light source 604 through the optical stack ofFIG. 1A in a public mode of operation.

The on-axis ray 410 of ambient light 604 traverses the plurality ofretarders 300 in a similar fashion to the on-axis ray 710 emitted fromthe emissive pixels 220, 222, 224 discussed above. Although the on-axisray 410 traverses the plurality of retarders 300 in the reversedirection to the on-axis ray 710 emitted from the emissive pixels 220,222, 224, the traversal of the plurality of retarders 300 in a reversedirection may not change the effect of the plurality of retarders 300 onthe light ray as discussed above for light emitted from the emissivepixels 220, 222, 224. The on-axis ray 410 therefore reaches the parallaxbarrier 700 absorption regions 704 whereon it is absorbed; or the pixellayer 214 whereon it may be absorbed or reflected as will be describedfurther below.

In a similar fashion, the off-axis ray 412 experiences no overalltransformation of polarisation state when passing through the pluralityof retarders 300. Ambient light 604 is unpolarised and the off-axislight ray initially has no polarisation 370. The additional polariser318 passes the polarisation component 372 that is parallel to theelectric vector transmission direction 319 of the additional polariser.The additional polariser 318 absorbs the majority of the polarisationstate 372 that is perpendicular to the electric vector transmissiondirection 319 of the additional polariser 318. Some light is reflectedfrom the front surface of the polariser 318 by Fresnel reflections atthe outer air interface. After traversing the plurality of retarders300, the linear polarisation state 374 of the off-axis ray 412 istherefore parallel to the electric vector transmission direction 303 ofthe reflective polariser 302 and the off-axis ray is not reflected butinstead passes the reflective polariser 302 to reach the parallaxbarrier 700 where it may be absorbed by the parallax barrier absorptionregions or transmitted to the pixel layer 214. Some of the reflectedlight rays 412 will be further absorbed by the absorption regions 704 ofthe parallax barrier 700 as further described below.

Advantageously the display reflectance in the public mode is reducedacross a wide range of viewing angles. Multiple users may convenientlyview the display from a wide range of viewing angles with high imagecontrast.

FIG. 10C is a schematic diagram illustrating in side view propagation ofoutput light from a spatial light modulator 48 through the optical stackof FIG. 1A in a privacy mode of operation.

In the privacy mode, the switchable liquid crystal retarder 301 is inthe on state where a voltage is applied to the liquid crystal layer 314.The switchable liquid crystal retarder 301 may therefore be in thesecond state of the said two states. In the case where the switchableliquid crystal retarder 301 has a positive dielectric anisotropy, theswitchable liquid crystal retarder 301 therefore acts in the secondstate in a similar manner to adjust the phase of the incidentpolarisation state that is output. The on-axis light ray 710 experiencesno retardation when passing through the switchable liquid crystalretarder 301 in the second state, and therefore the linear polarisationstate 360 of the on-axis light ray 710 prior to traversing the pluralityof retarders 300 is the same as the linear polarisation state 362 aftertraversing the plurality of retarders 300. The on-axis ray 710 thereforeexits the display via the additional polariser 318 with a largelyunchanged luminance in the privacy mode of operation.

Off-axis light rays 726 emitted from the emissive pixels 220, 222, 224and transmitted through aperture 702 of the barrier 700 experiences atransformation of polarisation when passing through the material of theswitchable liquid crystal retarder 301. This is because of the acuteangle of entry of the off-axis light ray 726. The off-axis light ray 726therefore arrives at the additional polariser 318 with a linearpolarisation state 364 that is at least partially rotated when comparedto the linear polarisation state 361. The linear polarisation state 364has at least some perpendicular component to the electric vectortransmission direction 319 of the additional polariser 318 and theluminance of the off-axis light ray 726 is therefore reduced compared tothe on-axis ray 710.

Advantageously the display luminance at wide viewing angles may bereduced in the second state. Snoopers may therefore be prevented fromviewing the image emitted by the display device 100 at wide viewingangles. Stray light may be reduced in night-time operation while thehead-on user may see an image.

FIG. 10D is a schematic diagram illustrating in side view propagation oflight rays from an ambient light source 604 through the optical stack ofFIG. 1A in a privacy mode of operation.

In privacy mode operation, incident on-axis light rays 410 from theambient light source 604 traverse the plurality of retarders 300 in asimilar fashion to the on-axis ray 710 emitted from the emissive pixels220, 222, 224 as described in relation to FIG. 10C. Although the on-axisray 410 traverses the plurality of retarders 300 in the reversedirection to the on-axis ray 710 emitted from the emissive pixels 220,222, 224, the direction of traversal of the plurality of retarders 300into or out of the display does not change the effect of the pluralityof retarders 300 on the light ray as discussed for light emitted fromthe emissive pixels 220, 222, 224. The on-axis ray 410 therefore reachesthe parallax barrier 700 where it may be absorbed by the parallaxbarrier absorption regions or transmitted to the pixel layer 214. Someof the reflected light rays 412 will be further absorbed by theabsorption regions 704 of the parallax barrier 700 as further describedbelow.

In contrast to this, off-axis light rays 412 experience a transformationof polarisation when passing through the material 414 of the switchableliquid crystal retarder 301. This is because of the acute angle of entryof the off-axis light ray 412, as discussed in further detail below. Theoff-axis light ray 412 therefore arrives at the reflective polariser 302with a linear polarisation state 374 that is at least partially rotatedwhen compared to the linear polarisation state 372. The linearpolarisation state 374 has at least some perpendicular state to theelectric vector transmission direction 303 of the reflective polariser302 and is therefore at least partially reflected by the reflectivepolariser 302. The ray 412 then traverses the plurality of retarders 300in the reverse direction, reversing the polarisation conversion from thefirst pass of the plurality of retarders 300 and resulting in apolarisation state 376 that is parallel to the electric vectortransmission direction of the additional polariser 318. The off-axis ray412 therefore leaves the display device 100 with polarisation state 378,resulting in the stack appearing as a mirror when viewed from awide-angle. The additional polariser 318 absorbs the majority of thepolarisation state 372 that is perpendicular to the electric vectortransmission direction 319 of the additional polariser, but may reflecta small proportion of the perpendicular state 404.

Advantageously the reflectance at wide viewing angles may be increasedin the second state. Snoopers may therefore be prevented from viewingthe image emitted by the display device 100 at wide viewing angles dueto the reflected light reducing the contrast of the image being emittedby the display device, and so increasing visual security level, VSL asdescribed in eqn. 7, above due to increased reflectivity, R.

Features of the arrangements of FIGS. 10A-D not discussed in furtherdetail may be assumed to correspond to the features with equivalentreference numerals as discussed above, including any potentialvariations in the features.

The simulated output of an illustrative embodiment will now bedescribed.

FIG. 11A is a polar plot array for the component contributions andoutput of the arrangement of FIG. 1A comprising polar plots for spatiallight modulator 48 luminance, parallax barrier 700 transmission,switchable retarder 300 transmission, normalised switchable retarder 300reflection, public mode luminance, privacy mode luminance and visualsecurity level for a lux/nit ratio of 1.0; and FIG. 11B is a linearprofile plot array for the component contributions and output of thearrangements of FIG. 11A comprising linear profiles at azimuthal anglesof 0 degrees (Eastern direction), 90 degrees (Northern direction), 45degrees (North Eastern direction) and 225 degrees (South Westerndirection). For purposes of the current description, the azimuthalorientations of the profiles in FIG. 11B are illustrated on the SLMluminance plot of FIG. 11A.

Illustrative parallax barrier 700 and OLED pixel parameters for FIGS.11A-B are provided in the first row of TABLE 4 with reference to thepitch, p of 50 μm in the direction in which the pixels are closest. Thepixels 220, 222, 224 are provided in the diamond arrangement of FIG. 4 .The direction in which the pixels are closest is for an azimuth of 45degrees.

TABLE 4 Pixel Pixel Aperture, Thickness, Compensated Lux/nit FIGS.pitch, p width, w a d LC retarder ratio 11A-B 50 μm 25 μm 27.5 μm 32.5μm See TABLE 3 1.0 11C 50 μm 25 μm 27.5 μm 32.5 μm See TABLE 3 0.2512A-B 50 μm 25 μm None None See TABLE 3 1.0 13A-B 50 μm 25 μm   25 μm50.0 μm None 1.0

A peak eQM reflectivity of 36% is used which corresponds to the 100%contour on the plot of normalised switchable retarder reflection aftertaking into account polariser 318 transmission and reflective polariser302 reflectance to polarised light.

The SLM 48 luminance plot illustrates that OLED displays provide anon-Lambertian luminance roll-off typically with greater than 20% ofhead-on luminance provided at polar angles of 50 degrees.

The parallax barrier 700 transmission plot illustrates the difference inprofiles for 0 degrees and 45 degrees azimuths due to the differentseparations of the pixels in this orientation.

The switchable retarder 300 transmission and reflectivity plotsillustrate the control of phase is along the lateral direction using thestructure of FIG. 9 .

The public mode illuminance is determined by the transmission by theparallax barrier 700 of the light from the spatial light modulator 48.The switchable polar control retarder 300 provides only a smallmodulation of this luminance profile.

The privacy mode luminance illustrates that less than 1% luminance isprovide in the lateral direction and in upper viewing quadrants. Thedisplay has high visibility for 0 degrees lateral angle and forrotations about the horizontal axis. Advantageously a comfortableviewing angle may be set for viewing the display from an on-axisposition by the user.

The effect of ambient light level on visual security level will now bedescribed.

FIG. 11C is a polar profile plot and linear polar profile plot for theillustrative embodiment of FIGS. 11A-B with a lux/nit ratio of 0.25. Thedisplay 100 properties are described in the second row of TABLE 4.

The visual security level (VSL) plots are dependent on the ambientilluminance condition. The ambient illuminance is provided as a ratio ofhead-on luminance. Thus in a typical office environment a display with300 nit head-on luminance and ambient illuminance falling on to thedisplay of 300 lux has a lux/nit ratio of 1.0. In a darkened aircraftcabin, a head-on luminance of 100 nits may be provided for an ambientilluminance of 25 nits, providing a lux/nit ratio of 0.25.

The switchable reflectivity of the present embodiment achieves increasedvisual security level at low lux/nit ratios. Further the parallaxbarrier 700 may further reduce the off-axis luminance to advantageouslyachieve further increased visual security in low illuminance conditions.

It has been determined by means of experiment and simulation that avisual security level in privacy mode of greater than 3.0 and preferablygreater than 4.0 is desirable for high isolation of the displayed imageto an off-axis snooper. It has also been determined by means ofexperiment and simulation that an image visibility W of greater than 50%and preferably greater than 83.3% (visual security level V in publicmode of less than 2.0 and preferably less than 1.2) achieves desirableimage visibility of the displayed image to an off-axis user.

The visual security level line profiles of FIGS. 11B-C illustrate that avisual security level of greater than 4.0 may be achieved for lateralangles and in viewing quadrants at lateral angles of at least 45 degreesand for azimuthal angles in the lateral direction and in the viewingquadrants in illumination conditions of less than 0.25 lux/nit.Advantageously high visual security level may be achieved for off-axisusers over a wide range of polar locations. The visual security leveldoes not degrade at higher polar angles in the lateral direction.

By way of comparison with the present embodiments, the simulatedappearance of the arrangement of FIG. 1A omitting the parallax barrier700 will now be described.

FIG. 12A is a polar plot array for the component contributions andoutput of the arrangement of FIG. 1A for an illustrative arrangement inwhich the parallax barrier 700 is removed comprising polar plots forspatial light modulator 48 luminance, parallax barrier 700 transmission,switchable retarder transmission, switchable retarder reflection, publicmode luminance, privacy mode luminance and visual security level at 1.0lux/nit; and FIG. 12B is a linear profile plot array for the componentcontributions and output of the arrangements of FIG. 12A comprisinglinear profiles at azimuthal angles of 0, 90, 45 and 225 degrees. Thedisplay 100 properties are described in the third row of TABLE 4.

By way of comparison with the present embodiments as will be describedin FIGS. 12A-B the polar control retarders 300 may not achieve desirablevisual security levels in displays with the high off-axis luminancelevels as are typically provided by emissive spatial light modulators 48in which the parallax barrier 700 is not present.

Considering the linear polar profile plot of visual security level inthe lateral (0 degrees) direction at angles of greater than 60 degrees,the VSL falls below 4.0 for 1.0 lux/nit. Such an arrangement providesundesirable visual security to an off-axis snooper despite having highVSL at angles around 45 degrees.

By way of comparison with the present embodiments, the simulatedappearance of the arrangement of FIG. 1A omitting the polar controlretarder 300 will now be described.

FIG. 13A is a polar plot array for the component contributions andoutput of the arrangement of FIG. 1A for an illustrative arrangement inwhich the switchable retarder is removed comprising polar plots forspatial light modulator 48 luminance, parallax barrier 700 transmission,switchable retarder transmission, switchable retarder reflection, publicmode luminance, privacy mode luminance and visual security level for 1.0lux/nit; and FIG. 13B is a linear profile plot array for the componentcontributions and output of the arrangements of FIG. 13A comprisinglinear profiles at azimuthal angles of 0, 90, 45 and 225 degrees.

The display 100 properties are described in the fourth row of TABLE 4.The parallax barrier thickness 700 is designed to be the minimumthickness to provide a VSL of greater than 4.0 at at least one azimuthfor a polar angle of 45 degrees in the lateral direction.

Such a display has undesirable privacy performance over a wide range ofpolar viewing angles and in particular viewing quadrants withoutsubstantial reduction in aperture size and subsequent undesirable lossof transmission efficiency.

The spectral transmission and spectral reflection of ambient light fromsurfaces of the display 100 of FIG. 1A in public mode of operation willnow be considered further.

FIG. 14 is a schematic diagram illustrating in side view reflection ofambient light in the display 100 of FIG. 1A. Features of the arrangementof FIG. 14 not discussed in further detail may be assumed to correspondto the features with equivalent reference numerals as discussed above,including any potential variations in the features.

Light rays 710 are passed by linear polarisers 218, 318 with a spectralmodification of light from the pixels 220, 222, 224 provided by thespectral transmission of the polarisers 218, 318.

Light rays 714, 715 that are internally reflected from the outer surfaceof the display 100. Light rays 714 are absorbed at incidence aredirected onto the parallax barrier 700 absorbing regions 704. Light rays715 are reflected from the reflective pixel layer 214. The reflectionreduction quarter-wave retarder 228 provides circular polarisation state442 that undergoes a phase change at reflection to provide circularpolarisation state 444 after reflection which is converted to apolarisation state that is orthogonal to the direction 219 and isabsorbed.

Thus light rays 714, 715 undergo two or three passes by polarisers 218,318, the spectral absorption modified accordingly.

The parallax barrier 700 is arranged to absorb light incident thereon.Light rays 410 from ambient source 604 are passed by polarisers 218, 318and absorbed by barrier regions 704. Light rays 412 that pass throughthe barrier and are reflected may be absorbed by the barrier afterreflection. The display 100 device is for use in ambient illumination604 and the parallax barrier 700 absorbs at least some of the ambientillumination 604 light rays 412 transmitted through the apertures 702that is reflected from the pixel layer 214.

It would be desirable to increase the spectral transmission of thedisplay 100 of FIG. 1A. Further it would be desirable to increase bluetransmission while not degrading appearance of display reflections.

FIG. 15 is a schematic graph illustrating the variation of outputluminance with wavelength for a case that the additional polariser 318is a broadband absorbing polariser and for a case that the additionalpolariser 318 is a leaking absorbing polariser. Profile 870 illustratesthe variation of transmitted luminance by parallel broadband polarisers;profile 872 illustrates the variation of transmitted luminance byparallel leaking polarisers; profile 874 illustrates the variation oftransmitted luminance by crossed broadband polarisers; and profile 876illustrates the variation of transmitted luminance by crossed leakingpolarisers. The leaking polariser 318 has increased leakage in the bluespectral band and increased transmission.

The output polariser 218 and additional polariser 318 when crossed witha second notional polariser of the same material has transmission forwavelengths from 520 nm to 560 nm that is less than the transmission forwavelengths from 450 nm to 490 nm. The transmission for wavelengths from450 nm to 490 nm is greater than 1%, preferably greater than 2% and mostpreferably greater than 3%; and the transmission for wavelengths from520 nm to 560 nm is less than 3%, preferably less than 2% and mostpreferably less than 1%.

The operation of the display 100 of FIG. 1A when using leakingpolarisers will now be described.

FIG. 16A is a schematic graph illustrating the variation of polariser218, 318 transmission with wavelength for broadband absorbing polarisersand for leaking absorbing polarisers and with respect to the spectraloutputs 890R, 890G, 890B of red, green and blue emitting pixels 220,222, 224 for transmitted rays 710 of FIG. 14 .

Profile 882 illustrates the spectral transmission of the embodiment ofFIG. 1A comprising leaking polarisers 218, 318.

By way of comparison with the present embodiment, profile 880illustrates the spectral transmission of the embodiment of FIG. 1Acomprising broadband absorbing polarisers 218, 318. Advantageously thepresent embodiment illustrated by profile 882 achieves substantiallyhigher transmission in the red, green and blue channels in comparison toarrangements comprising broadband polarisers 218, 318.

By way of further comparison with the present embodiments, profile 870illustrates the spectral output of a display that comprises a broadbandabsorbing polariser and broadband reflectance control quarter-waveretarder and does not comprise barrier 700, polar control retarder 300or additional polariser 318. Advantageously the present embodimentillustrated by profile 882 has substantially the same transmission forblue light as a display not comprising additional polariser 318.Efficient blue light emission provides increased lifetime for OLEDdisplays. Advantageously the present embodiment achieves the samedisplay lifetime as for conventional displays without additionalpolariser 318.

FIG. 16B is a schematic graph illustrating the variation of reflectancewith wavelength for broadband absorbing polarisers 218, 318 and forleaking absorbing polarisers 218, 318 and with respect to the spectraloutput 890R, 890G, 890B of red, green and blue emitting pixels 220, 222,224 for reflected rays of FIG. 14 .

Reflectance is determined at least in part by the transmission of lightrays 440 in FIG. 14 through polarisers 218, 318 after reflectionreduction quarter-wave retarder 228 and by absorption of parallaxbarrier 700.

To continue the illustrative embodiment of the first row of TABLE 4, theaperture ratio of the parallax barrier is 25% so that the barrierabsorption is 75% for light rays 410, 412 of FIG. 14 . Returning to theembodiment of FIG. 14 comprising leaking polarisers 218, 318 profile 888illustrates the average spectral transmission of the display integratedover viewing angles. Advantageously very low average reflectance may beprovided by the display. Further display efficiency is increased asillustrated in FIG. 16A.

Profile 884 illustrates the spectral transmission of the display of FIG.14 for light rays 440 that are both transmitted and reflected byaperture 702 of the parallax barrier 700. Profile 884 has significantlyimproved extinction in comparison to profile 876 with leakage at thepeak blue spectral wavelength of less than 1%. Advantageously, lowreflectivity is achieved.

By way of further comparison with the present embodiments, profile 886illustrates the spectral output of a display that comprises a broadbandabsorbing polariser and broadband reflectance control quarter-waveretarder and does not comprise barrier 700, polar control retarder 300or additional polariser 318. Such a display achieves low reflectanceover a wide spectral range but has reduced spectral transmission.

By way of further comparison with the present embodiments, profile 876illustrates the spectral output of a display that comprises a leakingabsorbing polariser and broadband reflectance control quarter-waveretarder and does not comprise barrier 700, polar control retarder 300or additional polariser 318. Such a display achieves low reflectanceover a wide spectral range. Such a display provides undesirablereflectance of light, particularly in the blue and green parts of thespectrum. Leaking polarisers with spectral transmission profiles 872,876 are thus not suitable for reflectance control in emissive displays.

The operation of embodiments comprising inorganic micro-LEDs will now bedescribed.

FIG. 17A is a schematic diagram illustrating in side perspective view aswitchable privacy display 100 for use in ambient illumination 604comprising a micro-LED emissive spatial light modulator 48, parallaxbarrier 700, output polariser 218 and reflection control quarter-waveretarder 228, passive polar control retarder 380, reflective polariser302, a switchable polar control retarder 300 and an additional polariser318 arranged on the output side of the spatial light modulator 48; andFIG. 17B is a schematic diagram illustrating in front view alignment ofoptical layers in the optical stack of FIG. 17A. Features of thearrangement of FIGS. 18A-B not discussed in further detail may beassumed to correspond to the features with equivalent reference numeralsas discussed above, including any potential variations in the features.

In comparison to OLED materials, pixels 220, 222, 224 comprisinginorganic micro-LEDs may have luminous emittance (lm/mm²) that is morethan 10³ greater. To achieve the same luminance the area of micro-LEDpixels 220, 222, 224 may be significantly smaller than that used forOLED pixels 220, 222, 224. Further smaller micro-LED pixels 220, 222,224 are lower cost due to reduced monolithic semiconductor area usage.For example micro-LEDs may have a width or diameter of less than 5micrometers for a pixel pitch of 50 micrometers in the direction inwhich the pixels are closest.

It would be desirable to achieve a public mode of operation with highimage visibility over a wide polar range and private mode with highvisual security level to off-axis snoopers.

The pixel layer 214 may comprise a light absorbing material 227 toadvantageously achieve reduced reflectance in comparison to thereflective pixel layer typical of OLED pixel layers 214 of FIG. 1A.

FIG. 17A further differs from FIG. 1A in comprising apertures 702 with acircular shape. Advantageously transmission profile symmetry may beincreased.

The pixels 220, 222, 224 are arranged on a square grid rather thandiamond grid. Such an arrangement provides for reduced luminance in thelateral direction with increased luminance in the quadrants.Advantageously visual security level in privacy mode may be increasedfor small elevations as will be illustrated below.

In embodiments (not shown) displays comprising mixtures of OLED andmicro-LED pixels may be provided (not shown). For example bluemicro-LEDs may be provided and green and blue OLED pixels.Advantageously blue lifetime may be increased and colour conversion formicro-LEDs is not used.

FIG. 17C is a schematic diagram illustrating in top view an arrangementof micro-LED emissive pixels 220, 222, 224 and eye spot locations forvarious polar viewing angles.

FIG. 17D is a schematic diagram illustrating in side perspective viewthe passive polar control retarder 380 arranged between the outputpolariser 218 and reflective polariser 302.

Passive polar control retarder 380 is arranged between the outputpolariser 218 and reflective polariser 302. The passive polar controlretarder 380 is capable of simultaneously introducing no net relativephase shift to orthogonal polarisation components of light rays passedby the output polariser 218 along an axis 199 along a normal to theplane of the at least one polar control retarder 380 and introducing arelative phase shift to orthogonal polarisation components of lightpassed by the reflective polariser 302 along an axis 197 inclined to anormal to the plane of the at least one polar control retarder 380.

The at least one passive retarder 380 comprises a retarder material 430having its optical axis 431 perpendicular to the plane of the retarder,the at least one passive retarder 330 having a retardance for light of awavelength of 550 nm in a range from −150 nm to −900 nm, preferably in arange from −200 nm to −500 nm and most preferably in a range from −250nm to −400 nm.

The operation of the passive polar control retarder 380 will bedescribed further below with regards to FIGS. 19A-B.

It would be desirable to optimise the spatial luminance uniformity ofthe display 100 comprising micro-LED pixels 220, 222, 224.

FIG. 18A is a schematic diagram illustrating in side view the structureof a spatial light modulator and aligned parallax barrier comprisingvignetted parallax barrier apertures.

The apertures 702 have an absorption that has a transmission gradient atthe edges of the aperture 702 that has a transmission gradient width sof greater than 1 micron, preferably greater than 2 microns and morepreferably greater than 3 microns.

In operation a point emitter 720 within the pixel 222 emits a sphericalwavefront 711 towards the aperture 702. On incidence at the aperture 702with the wavefront 711, residual wavefront curvature results in nearfield Fresnel diffraction such that rays 714 are provided at unintendedangles in the far field.

In parallax barriers with hard edges such that the transmission gradientwidth ε is smaller than 1 micron such rays may provide undesirable polarluminance variations from a point source and provide visible uniformityvariations that can be seen by an observer across the area of thedisplay 100.

In an illustrative micro-LED embodiment, the separation p of pixels maybe 50 micrometers and the pixel width may be 3 micrometers. In anillustrative OLED embodiment, the separation p of pixels may be 50micrometers and the pixel width may be 25 micrometers. In botharrangements the aperture 702 width a may be 16 micrometers. In displayswith organic emitters such as those illustrated in FIG. 1A, thediffracted rays are blurred due to the convolution with the large pixelarea. Advantageously high display uniformity may be achieved. Theconvolution blurring in OLED arrangements may be substantially greaterthan for micro-LED displays due to the small size of the micro-LEDemitters 220, 222, 224.

In the present embodiments, the transmission gradient width ε providesdiffractive apodisation of diffracted rays 714 in particular for smallemitting areas such as micro-LEDs in which substantial convolutionblurring is not provided. The luminance variations from the diffractedrays 714 are reduced by the transmission gradient width s.Advantageously the visibility of spatial luminance variations across thedisplay using micro-LED pixels 220, 222, 224 is reduced.

The transmission profile of various parallax barriers 700 will now befurther described.

FIGS. 18B-D are schematic graphs illustrating the variation of parallaxbarrier transmission with position for various parallax barrier 700structures.

FIG. 18B illustrates a first apodised transmission profile 701 ofrelative transmission against position in a direction θ at which theapertures are closest; wherein the absorption regions 704 have 100%absorption. The slope may be formed by thickness variations of absorbingmaterial and/or by half tone patterning across the width s.Advantageously luminance variations across the display may be minimised.Within the region of the width s of the slope of the profile 701 thetransmission varies to apodise the output as described with reference toFIG. 18A.

FIG. 18C illustrates increased transmission 705 for absorption regions704, for example by control of the thickness of the material used toform the absorption regions 704. The absorption of the region of theparallax barrier 700 between the apertures 702 is less than 100%, and isgreater than 80% preferably greater than 90% and more preferably greaterthan 95%. Transmission 705 may for example be less than 5% or less than2.5%. Advantageously increased luminance may be provided at higher polarviewing angles in public mode of operation.

FIG. 18D illustrates increased transmission for absorption regions 704by means of sub-aperture regions 722 as illustrated in FIG. 2A forexample. Average transmission 705 across the light absorbing regions 704may for example be less than 5% or less than 2.5%. Advantageouslyincreased luminance may be provided at higher polar viewing angles inpublic mode of operation.

The simulated output of an illustrative embodiment of FIG. 17A will nowbe described.

FIG. 19A is a polar plot array for the component contributions andoutput of the arrangement of FIG. 17A omitting the passive polar controlretarder 380 comprising polar plots for spatial light modulator 48luminance, parallax barrier 700 transmission, switchable retarder 300transmission, normalised switchable retarder 300 reflection, public modeluminance, privacy mode luminance and visual security level for alux/nit ratio of 1.0; and FIG. 19B is a linear profile plot array forthe component contributions and output of the arrangements of FIG. 19A.

Illustrative parallax barrier 700 and micro-LED pixel 220, 222, 224parameters for FIGS. 19A-B are provided in the first row of TABLE 5 withreference to the pitch, p of 50 μm in the direction in which the pixelsare closest. The pixels 220, 222, 224 are provided in the square packedarrangement of FIG. 17C and square parallax barrier 700 apertures 702are provided (in comparison to the illustrated circular apertures). Thedirection in which the pixels are closest is for an azimuth of 0degrees.

TABLE 5 Absorption Passive Pixel Pixel Aperture, region 704 Thickness,retarder Compensated Lux/nit FIGS. pitch, p width, w a transmission d330 LC retarder ratio 19A-B 50 μm 5 μm 20 μm 5% 27.5 μm None See TABLE 31.0 19C-D 50 μm 5 μm 20 μm 5% 27.5 μm C See TABLE 3 1.0 plate −350 nm20A-B 50 μm None None None None None See TABLE 3 1.0 21A-B 50 μm 5 μm 20μm 5% 27.5 μm None None 1.0 21C-D 50 μm 5 μm 20 μm 0% 27.5 μm None None1.0

In comparison to the output of FIG. 11A, the luminance profile from themicro-LED pixels 220, 222, 224 is illustrated as Lambertian and thushigher levels of luminance are provided at higher polar angles.

The polar output profile from the parallax barrier 700 has a highcentral output region and then slopes to 5% luminance at high polarangles using for example the arrangements of FIG. 2A. Advantageously thepublic mode of operation retains desirable image visibility at highviewing angles.

The slope of the luminance roll-off in public mode is determined by theprofile of the barrier edge which in the present illustrative embodimentis hard-edged. The soft-edged parallax barriers of FIGS. 18A-D mayfurther achieve a smoother roll-off of luminance profile in public modeof operation. Advantageously luminance uniformity for head-on use, anduniformity for off-axis polar viewing regions is improved.

In privacy mode of operation, advantageously a visual security level ofgreater than 4.0 is achieved for polar angles above 45 degrees and inparticular in the viewing quadrants. In other embodiments, not shown,the visual security level may be further increased by reducing thetransmission level of the parallax barrier 700 absorption regions 704.

It may be desirable to provide further luminance reduction in theviewing quadrants.

FIG. 19C is a polar plot array for the component contributions andoutput of the arrangement of FIG. 17A comprising polar plots for spatiallight modulator 48 luminance, parallax barrier 700 light absorbingregion 704 transmission, passive polar control retarder 380transmission, switchable retarder 300 transmission, switchable retarder300 reflection, public mode luminance, privacy mode luminance and visualsecurity level; and FIG. 19D is a linear profile plot array for thecomponent contributions and output of the arrangements of FIG. 19Ccomprising linear profiles at azimuthal angles of 0, 90, 45 and 225degrees. The display 100 properties are described in the second row ofTABLE 5. The passive polar control retarder 380 reduces the luminance inthe viewing quadrants. Advantageously the visual security levels in theviewing quadrants may be improved.

By way of comparison with the present embodiments, the simulatedappearance of the arrangement of FIG. 17A omitting the parallax barrier700 and polar control retarder 380 will now be described.

FIG. 20A is a polar plot array for the component contributions andoutput of the arrangement of FIG. 17A for an illustrative arrangement inwhich the parallax barrier 700 is removed comprising polar plots forspatial light modulator 48 luminance, parallax barrier 700 lightabsorbing region 704 transmission, switchable retarder 300 transmission,switchable retarder 300 reflection, public mode luminance, privacy modeluminance and visual security level; and FIG. 20B is a linear profileplot array for the component contributions and output of thearrangements of FIG. 20A comprising linear profiles at azimuthal anglesof 0, 90, 45 and 225 degrees. The display 100 properties are describedin the third row of TABLE 5.

By way of comparison with the present embodiments the polar controlretarders 300 may not achieve desirable visual security levels indisplays with the high off-axis luminance levels as are typicallyprovided by emissive spatial light modulators 48 comprising micro-LEDsin which the parallax barrier 700 is not present.

Considering the linear polar profile plot of visual security level inthe lateral (0 degrees) direction at angles of greater than 60 degrees,the VSL remains below 4.0 for 1.0 lux/nit for almost all polar viewingangles. Such an arrangement provides undesirable visual security to anoff-axis snooper.

Byway of comparison with the present embodiments, the simulatedappearance of the arrangement of FIG. 1A omitting the polar controlretarders 300, 380 will now be described.

FIG. 21A is a polar plot array for the component contributions andoutput of the arrangement of FIG. 17A for an illustrative arrangement inwhich the switchable retarder 300 and passive polarisation controlretarder 380 are removed and the parallax barrier 700 providestransmission in the light absorbing regions 704; comprising polar plotsfor spatial light modulator 48 luminance, parallax barrier 700transmission, switchable retarder 300 transmission, switchable retarder300 reflection, public mode luminance, privacy mode luminance and visualsecurity level; and FIG. 21B is a linear profile plot array for thecomponent contributions and output of the arrangements of FIG. 21Acomprising linear profiles at azimuthal angles of 0, 90, 45 and 225degrees. The display 100 properties are described in the fourth row ofTABLE 5. To achieve desirable image visibility in public mode, theluminance at high polar viewing angles is 5%. However, the visualsecurity level is below 4.0 for all polar viewing angles and below 2.0for most polar viewing angles. Such a display does not provide asatisfactory privacy mode of operation.

FIG. 21C is a polar plot array for the component contributions andoutput of the arrangement of FIG. 17A for an illustrative arrangement inwhich the switchable retarder 300 and passive polarisation controlretarder 380 are omitted and the parallax barrier 700 provides notransmission in the light absorbing regions 704; comprising polar plotsfor spatial light modulator 48 luminance, parallax barrier 700transmission, switchable retarder 300 transmission, switchable retarder300 reflection, public mode luminance, privacy mode luminance and visualsecurity level; and FIG. 21D is a linear profile plot array for thecomponent contributions and output of the arrangements of FIG. 21Ccomprising linear profiles at azimuthal angles of 0, 90, 45 and 225degrees. The display 100 properties are described in the fifth row ofTABLE 5. To achieve desirable visual security level in privacy mode, theluminance at high polar viewing angles is 0%, that is the absorbingregions 704 are highly absorbing. However, there is no image visibilityfor polar viewing angles above about 45 degrees. Such a display does notprovide a satisfactory public mode of operation. Transmission levelsbetween 0% and 5% do not provide satisfactory trade-offs between privacyand public modes of operation.

Advantageously the present embodiments achieve high visual securitylevel over a wide polar range in privacy mode and achieve high imagevisibility of a wide polar range in public mode. Further high head-onimage visibility is achieved in both privacy and public modes ofoperation.

Further arrangements of polar control retarders will now be described.

FIG. 22A is a diagram illustrating in perspective side view anarrangement of a switchable retarder in a privacy mode wherein theswitchable retarder comprises a switchable LC layer with homogeneousalignment arranged between C-plate passive polar control retarders 330A,330B; and FIG. 22B is a diagram illustrating in perspective side view anarrangement of a switchable retarder in a public mode wherein theswitchable retarder comprises a switchable LC layer with homogeneousalignment arranged between C-plate passive polar control retarders 330A,330B. Features of the arrangement of FIGS. 22A-B not discussed infurther detail may be assumed to correspond to the features withequivalent reference numerals as discussed above, including anypotential variations in the features.

The retarders 330A, 330B may comprise the substrates for the switchableliquid crystal layer 314. Advantageously thickness may be reduced.Further, flexible substrates may be provided. The display 100 may beprovided in active flexible embodiments (bendable multiple times by theuser) or in passive flexible embodiments (bendable during manufacturing)to achieve free-form display profiles.

It would be desirable to provide displays that operate in landscape andportrait orientations for both privacy and public modes of operation.

FIG. 23A is a schematic diagram illustrating in perspective side view anarrangement of retarder layers arranged between parallel polarisers andcomprising a 270 degree super twisted switchable liquid crystal retarder301 arranged between quarter-wave plates. Features of the arrangementsof FIGS. 23A-C not discussed in further detail may be assumed tocorrespond to the features with equivalent reference numerals asdiscussed above, including any potential variations in the features.Further embodiments of polar control retarders that achieve symmetricpolar profiles are described in U.S. Patent Publ. No. 2020-0159055,which is herein incorporated by reference in its entirety.

First and second quarter-wave plates 296A, 296B are arranged between theadditional polariser 318 and the output polariser 218. The firstquarter-wave plate 296A is arranged on the input side of the secondquarter-wave plate 296B and is arranged to convert a linearly polarisedpolarisation state passed by the output polariser 218 on the input sidethereof into a circularly polarised polarisation state. The secondquarter-wave plate 296B on the output side being arranged to convert acircularly polarised polarisation state that is incident thereon into alinearly polarised polarisation state that is passed by the additionalpolariser 318 on the output side thereof. At least one retarder 301 isarranged between the pair of quarter-wave plates 296A, 296B.

The at least one polar control retarder 300 comprises a switchableliquid crystal retarder 301 comprising a layer of liquid crystalmaterial and electrodes arranged to apply a voltage for switching thelayer of liquid crystal material. The layer of liquid crystal materialhas a twist of 360 degrees and a retardance for light of a wavelength of550 nm in a range from 1100 nm to 1400 nm and most preferably in a rangefrom 1150 nm to 1300 nm.

The simulated output of an illustrative embodiment of FIG. 17Acomprising the switchable polar control retarder of FIG. 23A will now bedescribed.

FIG. 23B is a polar plot array for the component contributions andoutput of the arrangement of FIG. 17A omitting the passive polar controlretarder 380 comprising polar plots for spatial light modulator 48luminance, parallax barrier 700 transmission, switchable retarder 300transmission, normalised switchable retarder 300 reflection, public modeluminance, privacy mode luminance and visual security level for alux/nit ratio of 1.0; and FIG. 23C is a linear profile plot array forthe component contributions and output of the arrangements of FIG. 23A.

An illustrative liquid crystal retarder 300 is described in TABLE 6. Anillustrative parallax barrier 700 and OLED pixel 220, 222, 224 for FIGS.23B-C is described in TABLE 7 with reference to the pitch, p of 50 μm inthe direction in which the pixels are closest. The pixels 220, 222, 224are provided in the square packed arrangement of FIG. 4 and squareparallax barrier 700 apertures 702 are provided. The direction in whichthe pixels are closest is for an azimuth of 0 degrees.

TABLE 6 LC alignment Dielectric Quarter-wave layer 314 & LC LCretardance anisotropy 296A, 296B Polariser pretilt directions twist(desirable range) Δε Drive voltage retardance spectral profileHomogeneous 360° 1220 nm 10 Public mode  0 V 135 nm Leaking type45°/135° (1100 nm~1400 nm) Privacy mode 10 V profile 872, 876

TABLE 7 Absorption Passive Pixel Pixel Aperture, region 704 Thickness,retarder Compensated Lux/nit FIGS. pitch, p width, w a transmission d330 LC retarder ratio 23B-C 50 μm 25 μm 27.5 μm 0% 38.5 μm None SeeTABLE 6 1.0

Advantageously a rotationally symmetric privacy mode may be achieved incomparison to the laterally symmetric profiles achieved by theembodiments using polar control retarders 300 such as those of FIG. 9for example.

FIG. 24A is a schematic diagram illustrating in perspective views theappearance of luminance of a mobile device in public mode comprising thedisplay device 100 of FIG. 1A with the switchable polar control retarder300 of FIG. 23 with appearance shown in order from top left clockwise:head-on landscape, head-on portrait, look-down portrait andlook-from-right landscape.

The viewing direction along axis 199 of the display device 100 isperpendicular to the viewing surface of the display device 100. In allthe orientations shown, in public mode the image being emitted by thedisplay device 100 is visible to an observer as represented by the whitecolouring representing the image emitted by the display device 100. Theimage is visible in all of an on-axis landscape and portrait orientation520, a look-down portrait orientation 522 and a look-from-rightlandscape orientation 528.

FIG. 24B is a schematic diagram illustrating in perspective views theappearance of luminance of a mobile device in privacy mode comprisingthe display device 100 of FIG. 1A with the switchable polar controlretarder 300 of FIG. 23 with appearance shown in order from top leftclockwise: head-on landscape, head-on portrait, look-down portrait andlook-from-right landscape.

In the privacy mode, the view to an observer remains unchanged in theon-axis landscape and portrait orientation 520 and the image emitted bythe display device 100 is visible to an observer. However, in thelook-down portrait orientation 522 and the look-from-right landscapeorientation 528 the image emitted by the display device is no longervisible. A snooper observing from a wide-angle instead observes amirror-like surface provided by the reflective polariser 302 asdescribed above.

FIG. 24C is a schematic diagram illustrating in perspective views theappearance of reflectivity of a mobile device in privacy mode comprisingthe display device 100 of FIG. 1A with the switchable polar controlretarder 300 of FIG. 23 with appearance shown in order from top leftclockwise: head-on landscape, head-on portrait, look-down portrait andlook-from-right landscape.

In the privacy mode, the view to an observer remains unchanged in theon-axis landscape and portrait orientation 520 as the reflectivity fromthe additional polariser 318 is minimal. However, in the look-downportrait orientation 522 and the look-from-right landscape orientation528, reflections from the surface of the additional polariser 318 mayresult in frontal reflections as described above, desirably increasingvisual security level, VSL.

FIG. 25A is a schematic diagram illustrating in top view an automotivevehicle 600 with a switchable directional display 100 arranged withinthe vehicle cabin 602 in a night mode of operation.

The night mode of the switchable directional display 100 may correspondto the privacy mode discussed above. A light cone 620 (for examplerepresenting the cone of light within which the luminance is greaterthan 50% of the peak luminance emitted by the switchable directionaldisplay 100) may indicate the range of angles in which the image emittedby the switchable directional display 100 is discernible. As shown inFIG. 25A, when the switchable directional display 100 is in night mode,the driver 604 falls within the area defined by the light cone 620 in ahorizontal direction and the image emitted by the switchable directionaldisplay 100 is therefore discernible to the driver 604. In contrast tothis, high-angle light rays 622 falling outside the light cone 620 in ahorizontal direction have a reduced luminance and the image emitted bythe switchable directional display 100 therefore may not be discernibleto a passenger 608 in the vehicle 600. This may be advantageous if thepassenger is attempting to sleep or relax during the night.

In such an arrangement, the reflective polariser 302 may be omitted ifsome image visibility to other users is acceptable. Advantageouslydisplay efficiency may be increased and visibility of stray lightreduced.

FIG. 25B is a schematic diagram illustrating in side view an automotivevehicle 600 with a switchable directional display 100 arranged withinthe vehicle cabin 602 in a night mode of operation.

In night mode, the volume 606 occupied by the face of the driver fallswithin the area defined by the light cone 620 in a vertical directionand the image emitted by the switchable directional display 100 istherefore discernible to the driver in volume 606. However, high-anglelight rays 622 falling outside the light cone 620 in a verticaldirection may have a reduced luminance in night mode operation. Theluminance of high-angle light rays 622 that may reflect off of thewindscreen 618 of the automotive vehicle 600 may be reduced. Thisadvantageously may reduce the reflections of the display 100 perceivedon the windscreen 618 by the driver in volume 606.

It would be desirable to provide increased uniformity for rotation ofthe display 100 about a horizontal axis and to relax alignmenttolerances between the parallax barrier 700 and pixel layer 214.

FIG. 26 is a schematic diagram illustrating in side perspective view aswitchable privacy display 100 for use in ambient illumination 604comprising an OLED emissive spatial light modulator 48, one dimensionalparallax barrier 700, output polariser 218 and reflection controlquarter-wave retarder 228, a reflective polariser 302, a switchablepolar control retarder 300 and an additional polariser 318 arranged onthe output side of the spatial light modulator 48; and FIG. 27 is aschematic diagram illustrating in front view alignment of optical layersin the optical stack of FIG. 26 . Features of the arrangement of FIGS.26-27 not discussed in further detail may be assumed to correspond tothe features with equivalent reference numerals as discussed above,including any potential variations in the features.

The polar control retarder 300 is as illustrated in FIGS. 22A-B.

The parallax barrier 700 forms a one dimensional array of apertures 702,the pixels 220, 222, 224 being arranged in columns, each column ofpixels 220, 222, 224 being aligned with a respective aperture.

Pixel 220, 222, 224 has a light emission region that is extended in thedirection in which the apertures 702 are extended; the width of the red,green and blue light emission regions are the same for each of thepixels 220, 222, 224; and the height of the light emission regions aredifferent for red, green and blue light emitting pixels 220, 222, 224.

Advantageously a switchable privacy display may be provided with highimage visibility for off-axis users in a lateral direction and highvisual security for off-axis snoopers in a lateral direction in publicand privacy modes respectively. Viewing freedom for rotation about ahorizontal axis may be increased. Advantageously the head-on userlocation may be conveniently adjusted in the elevation direction withhigh luminance uniformity.

Further the alignment of the parallax barrier 700 to the pixel layer maybe controlled in lateral and orientation axes only in comparison to thearrangement of FIG. 1A wherein the alignment is controlled in lateral,vertical and orientation axes. Advantageously yield may be increased andcost reduced.

It would be desirable to increase the efficiency of the display 100while providing low reflectivity of light from the reflective pixellayer 214.

FIG. 28 is a schematic diagram illustrating in side perspective view aswitchable privacy display 100 for use in ambient illumination 604comprising a micro-LED emissive spatial light modulator 48, parallaxbarrier 700, and output polariser 218 that is a reflective polariser302, reflection control quarter-wave retarder 228, a switchable polarcontrol retarder 300 and an additional polariser 318 arranged on theoutput side of the spatial light modulator 48; and FIG. 29 is aschematic diagram illustrating in side view reflection of ambient lightin the display 100 of FIG. 28 . Features of the arrangement of FIGS.28-29 not discussed in further detail may be assumed to correspond tothe features with equivalent reference numerals as discussed above,including any potential variations in the features.

In comparison to the arrangement of FIGS. 1A and 17A, a reflectiveoutput polariser 218302 is provided. The absorptive polariser 218 isomitted so that the transmission of the display is advantageouslyincreased, achieving increased luminance and reduced power consumptionfor a desirable image luminance.

In comparison to the embodiment of FIG. 14 , light ray 760 from ambientlight source 604 has a polarisation state that is substantiallyreflected from the reflective output polariser 218302 to provide ray762, which is absorbed by absorptive regions 704 of the parallax barrier700. Light rays 764 that are transmitted by the reflective polariser218302 are absorbed by polariser 318. Advantageously reflection ofambient light rays 760 is reduced.

It would be desirable to provide a low reflectivity display with highefficiency.

FIG. 30 is a schematic diagram illustrating in side perspective view alow reflectivity display 200 for use in ambient illumination 604comprising an OLED emissive spatial light modulator 48, two dimensionalparallax barrier 700, leaking output polariser 218 and reflectioncontrol quarter-wave retarder 228 arranged on the output side of thespatial light modulator 48; and FIG. 31 is a schematic diagramillustrating in side view reflection of ambient light in the display 200of FIG. 30 . Features of the arrangement of FIGS. 30-31 not discussed infurther detail may be assumed to correspond to the features withequivalent reference numerals as discussed above, including anypotential variations in the features.

A reflectivity control display 200 device for use in ambientillumination comprises the display 200 wherein the parallax barrier 700absorbs at least some of the ambient illumination 604.

In comparison to the arrangement of FIG. 1A, the display 200 is notprovided as a privacy display 100. The output may be provided forexample as illustrated in FIGS. 21A-B and in the illustrative embodimentof the fourth row of TABLE 5 such that the aperture ratio of theapertures 702 is 25% and the transmission of the absorbing regions 704of the parallax barrier 700 is 5%. The polariser 218 comprises a leakingpolariser such as illustrated in FIG. 15 . Advantageously outputefficiency in the head-on direction is increased in comparison toarrangements with a high extinction type polariser.

It would be desirable to provide a touch sensor for a low reflectivitydisplay 200.

FIG. 32 is a schematic diagram illustrating in side perspective view atouch screen low reflectivity display 200 for use in ambientillumination 604 comprising an OLED emissive spatial light modulator 48,two dimensional parallax barrier 700 comprising touch sensor electrodelayers, leaking output polariser 218 and reflection control quarter-waveretarder 228 arranged on the output side of the spatial light modulator48; FIG. 33 is a schematic diagram illustrating in front view reflectionof ambient light in the display 200 of FIG. 32 ; and FIG. 34 is aschematic diagram illustrating in side view the structure of FIG. 32 .Features of the arrangement of FIGS. 32-34 not discussed in furtherdetail may be assumed to correspond to the features with equivalentreference numerals as discussed above, including any potentialvariations in the features.

The array of apertures 702 are formed on a touch sensor electrode array500. Finger 25 location at or near a protective cover layer 320 isdetected by means of the touch electrode arrays 500, 502, touch drivers452, 454 and touch control system 450. The touch electrode array 500,may be formed on the surface of the parallax barrier 700 or on thesurface of the quarter-wave retarder.

The pair of touch electrode arrays 500, 502 are arranged in layersseparated by dielectric layer 504. The dielectric layer 504 is arrangedbetween the switchable liquid crystal layer 314 and the additionalpolariser 318. The first and second touch electrode arrays 500, 502 arearranged on the dielectric layer 504 and on opposite sides of thedielectric layer 504.

The touch electrode arrays 500, 502 are arranged between the pixel layer214 and parallax barrier 700 or as illustrated in FIG. 32 between theparallax barrier 700 and quarter-wave reflection control retarder 228.

The touch input display device 100 further comprises a control system450, wherein the control system 450 is arranged to address the touchelectrode arrays 500, 502 for capacitive touch sensing.

The control system 450 is further arranged to address the SLM 48. Thecontrol system comprises a system controller that is arranged to controlthe signal applied to and measured from the touch electrode arrays 500,502 by means of touch drivers 452, 454.

The electrodes 500, 502 are arranged between the apertures 702 of theparallax barrier. Advantageously high efficiency may be achieved.

In other embodiments as illustrated in FIG. 34 the at least oneabsorbing region 704 of the parallax barrier 700 comprises a touchsensor electrode array 502. Advantageously the touch sensor electrodearrays 500, 502 may have reduced reflectivity. Further touch electrodes504 may be provided at the pixel layer 214.

In other embodiments (not shown) a touch sensing electrode layer may bearranged at the pixel layer 214. Advantageously the control of thesensing electrodes may be provided with the control of the pixel data,reducing cost and complexity.

It would be further desirable to achieve increased transmissionefficiency.

FIG. 35A is a schematic diagram illustrating in side perspective view alow reflectivity display 200 for use in ambient illumination 604comprising an OLED emissive spatial light modulator 48, two dimensionalparallax barrier 700 and no output polariser arranged on the output sideof the spatial light modulator 48; and FIG. 35B is a schematic diagramillustrating in side view reflection of ambient light in the display 200of FIG. 35A. Features of the arrangement of FIGS. 35A-B not discussed infurther detail may be assumed to correspond to the features withequivalent reference numerals as discussed above, including anypotential variations in the features.

In comparison to the embodiment of FIG. 30 , the output polariser 218 isomitted. Advantageously efficiency is increased.

Ambient light rays 410, 412 are absorbed by absorption regions 704 whileoutput rays 710 in the normal are transmitted without loss. High anglelight rays 712 from pixel 220 are further absorbed. Thus some ambientlight rays are absorbed, advantageously increasing image contrast.

It would be desirable to further reduce reflectivity of ambient lightrays.

FIG. 36A is a schematic diagram illustrating in side perspective view alow reflectivity display for use in ambient illumination comprising anOLED emissive spatial light modulator, two one-dimensional parallaxbarriers 700A, 700B and no output polariser arranged on the output sideof the spatial light modulator 48; and FIG. 36B is a schematic diagramillustrating in side view reflection of ambient light in the display ofFIG. 36A. Features of the arrangement of FIGS. 36A-B not discussed infurther detail may be assumed to correspond to the features withequivalent reference numerals as discussed above, including anypotential variations in the features.

The barriers 700A, 700B may be arranged on separate substrates 216A,216B that provide a separation of the barriers. Light may be trappedwithin the substrate 216B and absorbed.

In comparison to the embodiments of FIGS. 35A-B, the alignment tolerancefor each barrier 700A, 700B may be relaxed, increasing yield andreducing cost. Further additional high light rays 713 may be absorbedreducing leakage between pixels. Advantageously image contrast may beincreased.

It may be desirable to reduce off-axis light from emissive pixels andincrease efficiency directed into the forwards direction.

FIG. 37A is a schematic diagram illustrating in side view a catadioptricoptical element array arranged between the pixels 220, 222, 224 of thespatial light modulator 48 and the parallax barrier 700; and FIG. 37B isa schematic graph illustrating the variation of output luminance withpolar angle for the arrangement of FIG. 37A. Features of the arrangementof FIG. 37A not discussed in further detail may be assumed to correspondto the features with equivalent reference numerals as discussed above,including any potential variations in the features.

Catadioptric optical elements for emissive displays are described inWIPO Publ. No. WO 2019/138243, which is herein incorporated by referencein its entirety.

Catadioptric optical structure 800 is aligned with the emissive pixels220, 222, 224 to provide a directional light output distribution fromthe spatial light modulator 48 that is similar to that illustrated inFIG. 11A or FIG. 19A. The catadioptric optical structure 800 comprises aplurality of catadioptric optical elements 838 arranged in acatadioptric optical element array, each of the catadioptric opticalelements 838 of the plurality of catadioptric optical elements 800aligned in correspondence with a respective one or more of the pixels ofthe plurality of pixels 220, 222, 224, each of the pixels of theplurality of LEDs being aligned with only a respective one of thecatadioptric optical elements 838 of the catadioptric optical structure800.

Each of the plurality of catadioptric optical elements 838 comprises inat least one catadioptric cross-sectional plane through its optical axis199 a first cross-sectional outer interface 804A and a secondcross-sectional outer interface 804B facing the first cross-sectionalouter interface 804A.

The first and second cross-sectional outer interfaces 804A, 804B eachcomprise curved interfaces comprising first and second outer interfaceregions 840, 842.

The first and second cross-sectional outer interfaces 804A, 804B extendfrom a first end of the catadioptric optical element 838 to a second endof the catadioptric optical element 838, the second end of thecatadioptric optical element 838 facing the first end of thecatadioptric element.

The distance between the first and second cross-sectional outerinterfaces at the first end of the catadioptric optical element that isat the pixel layer is less than the distance between the first andsecond cross-sectional outer interfaces 804A, 804B at the second end ofthe catadioptric optical element 838 that is at the output side of thecatadioptric optical element 838.

At least one transparent inner interface 810 is arranged between thefirst and second ends and between the first and second outer interfaces804A, 804B.

The catadioptric optical structure 838 comprises: (i) a firsttransparent non-gaseous material with a first refractive index arrangedbetween the first and second cross-sectional outer interfaces and the atleast one transparent inner interface and between the first and secondend of each of the catadioptric optical elements; (ii) a secondtransparent non-gaseous material with a second refractive index lowerthan the first refractive index arranged between a respective alignedpixel 220, 222, 224 and the transparent inner interface of each of thecatadioptric optical elements; (iii) a third transparent non-gaseousmaterial with a third refractive index lower than the first refractiveindex arranged between the first cross-sectional outer interface of afirst catadioptric optical element and the second cross-sectional outerinterface of an adjacent catadioptric optical element of the pluralityof catadioptric optical elements and between the first and second end ofeach of the catadioptric optical elements.

The tilt angle with respect to the optical axis 199 of the interfacenormal of each of the first and second cross-sectional outer interfaces804A, 804B varies continuously with the distance c from the first endtowards the second end. The derivative of the tilt angle with respect todistance J from the optical axis 199 has a discontinuity at the boundary844 between the respective first and second outer interface regions 840,842 of the first and second cross-sectional outer interfaces 804A, 804B.

The materials 802, 814 may be transparent and conveniently provided inlayer 800, reducing manufacturing cost and complexity.

The present embodiments achieve encapsulation of an OLED pixel by meansof the solid catadioptric optical element 838 that has interfaces 804A,804B arranged to advantageously achieve directional illumination withlow levels of cross talk to snoopers. Profile 850 of FIG. 37B may beprovided by the illustrative embodiment of TABLE 8.

TABLE 8 Material 808 Material 802 Material 812 Critical Refractive indexRefractive index Refractive index angle/deg 1.60 1.38 1.38 59.6

Most of the principal rays 820 in the second outer interface region 842are directed in a direction that is close to parallel to the opticalaxis 199 by total internal reflection, providing high levels ofcollimation for light rays reflected from the outer surfaces 804A, 804B.Light rays 822 that are incident on the region 840 are directed indirections that are close to but not identical to the collimationdirection for known low cost materials in a solid catadioptric opticalelement 38.

Advantageously losses are reduced and efficiency is increased foron-axis light rays.

In other embodiments, the interfaces 804 may be provided by metallicsurfaces to provide some collimation of output light.

It would be desirable to reduce the number of rays at higher polarangles. Parallax barrier 700 absorption regions 704 may be arranged toreduce the luminance at higher polar angles.

In further embodiments, the shape of the surfaces 804A, 804B may bearranged to provide controlled light rays at high polar angles toachieve increased luminance at higher polar angles, for example between2.5% and 15% of head-on luminance. Public mode luminance may be providedwith high image visibility. Polarisers 218, 318 and polar controlretarders 300 may be arranged to achieve switching between public modeand privacy mode. Further pixels may be arranged on the pixel layerbetween in catadioptric optical elements 838 to achieve increased lightat high polar angles as described in WIPO Publ. No. WO 2018/185475,which is herein incorporated by reference in its entirety.

Methods to manufacture display apparatuses of the present embodimentswill now be described.

FIGS. 38A-D are schematic diagrams illustrating in side views a methodto manufacture a parallax barrier 700 for an emissive display 100, 200using a fine metal mask 900.

FIG. 38A illustrates in a first step the forming an array of emissivepixels 220, 222, 224 on a backplane by means of directing emissivematerials 802 through a fine metal mask. The structure of pixels 220,222, 224 is further described in FIG. 6 for example.

FIG. 38B illustrates in a second step the addition of inorganic layers752 and organic layers 750 to provide substrate 216 as an encapsulationlayer for the pixel layer 214. The step of forming an encapsulationlayer on the array of emissive pixels 220, 222, 224 thus comprisesforming at least one transparent inorganic layer 752. The at least onetransparent inorganic layer may be a glass layer. The glass layer may beprovided with the appropriate thickness d by means ofchemical-mechanical polishing of a thicker glass layer. The organiclayers 750 may be omitted. An adhesive layer 244 may be provided betweenthe pixel layer 214 and the substrate 216.

FIG. 38C illustrates forming the parallax barrier 700 comprising anarray of apertures 702 on the surface of the encapsulation layersubstrate 216 by directing light absorbing material 903 through a finemetal mask 904. The mask 904 may be the same as the mask 900. Thealignment of the mask 904 is displaced in lateral position with respectto the alignment of the mask 900 to achieve alignment of the apertures702 with the centre of the pixels 220, 222, 224.

FIG. 38D illustrates the barrier formed on the layer 216 prior toarranging layers such as further encapsulation layers, reflectionreduction retarder 228, polarisers 218, 318 and polar control retarder300 on the parallax barrier.

Advantageously the parallax barrier 700 may be formed using similarequipment and masking technologies used for forming the pixels 220, 222,224. Cost of applying parallax barriers 700 may be advantageouslyreduced.

The pixels 220, 222, 224 have a pitch p along the direction in which theapertures 702 are closest, the material between the parallax barrier 700and the pixels 220, 222, 224 has a bulk refractive index n and theencapsulation layer has a thickness d meeting the requirement that2d/p≤√(2n²−1). The apertures 702 have a width a along the direction inwhich the apertures 702 are closest, the material between the parallaxbarrier 700 and the pixels 220, 222, 224 has a bulk refractive index nand the encapsulation layer has a thickness d meeting the requirementthat d≥a√(n²−1)/2 and preferably meeting the requirement thatd≥an√(1−3/(4n²))/√3.

It would be desirable to provide the parallax barrier by means of highprecision lithography.

FIGS. 39A-F are schematic diagrams illustrating in side views a methodto manufacture a parallax barrier 700 for an emissive display usinglithography.

A method to form a display device comprising the steps of forming anarray of emissive pixels 220, 222, 224 on a backplane by means ofdirecting emissive materials through a fine metal mask forming anencapsulation layer on the array of emissive pixels 220, 222, 224comprising at least one transparent inorganic layer; forming theparallax barrier 700 comprising an array of apertures 702 on the surfaceof the encapsulation layer by means of lithographic patterning.

In the first and second steps the emissive display is provided asillustrated in FIGS. 38A-B.

FIG. 39A illustrates that in a third step barrier material 904 is formedon the upper surface of the layer 216.

FIG. 39B illustrates that in a fourth step a photolithographic maskingmaterial 906 is arranged on the upper surface of the material 904.

FIG. 39C illustrates that in a fifth step a photomask 908 is arranged inalignment with the pixels 220, 222, 224 and exposed to UV radiation 910.

FIG. 39D illustrates that in a sixth etch step the material 904 isremoved.

FIG. 39E illustrates that in a seventh step the photolithographicmaterial is removed.

FIG. 39F illustrates the final device after addition of a furtherencapsulation layer.

Advantageously a high resolution and accurately aligned parallax barriermay be provided, reducing cost and complexity and providing highestluminance in the normal direction aligned with axis 199.

It may be desirable to provide the parallax barrier on a separate layerand align with the spatial light modulator 48.

FIGS. 40A-D are schematic diagrams illustrating in side views a methodto manufacture a parallax barrier 700 for an emissive display 100, 200using printing.

FIG. 40A illustrates that parallax barrier 700 may be provided using aprinting method such as ink jet printing, lithography, flexography orother know printing technology to apply absorbing material in regions704. The parallax barrier 700 may be provided on substrate 110.

FIG. 40B illustrates that the parallax barrier may be aligned to thepixel layer 214. Material 246 is input into the gap between thesubstrate 216 and parallax barrier 700.

FIG. 40C illustrates the device structure after curing of the adhesivematerial 246.

FIG. 40D illustrates thinning of the substrate 110 for example bychemical-mechanical polishing of the substrate 110.

Advantageously the parallax barrier may be formed after fabrication ofthe emissive display.

Features of the arrangement of FIGS. 38A-D, FIGS. 39A-F and FIGS. 40A-Dnot discussed in further detail may be assumed to correspond to thefeatures with equivalent reference numerals as discussed above,including any potential variations in the features.

It would be desirable to provide an emissive privacy display withincreased head-on efficiency and reduced off-axis luminance.

FIG. 41 is a schematic diagram illustrating in side perspective view aswitchable privacy display 100 for use in ambient illuminationcomprising an OLED emissive spatial light modulator 48 comprisingprofiled OLED pixels 220, 222, 224, output polariser 218 and reflectioncontrol quarter-wave retarder 228, reflective polariser 302, aswitchable polar control retarder 300 and an additional polariser 318arranged on the output side of the spatial light modulator 48; and FIG.42 is a schematic diagram illustrating in side perspective view pixelsof an OLED emissive spatial light modulator 48 wherein the OLED pixels220, 222, 224 are profiled OLED pixels comprising profiled wells 272 anda high index filler material 270. Features of the arrangement of FIGS.41-42 not discussed in further detail may be assumed to correspond tothe features with equivalent reference numerals as discussed above andbelow, including any potential variations in the features.

The structure and operation of one of the pixels 220 will now bedescribed.

FIG. 43 is a schematic diagram illustrating in side view one pixel of anOLED emissive spatial light modulator wherein the OLED pixel comprisesprofiled wells 272 and a high index filler material 270. The pixel 220is driven by pixel circuitry 249 comprising electrodes 243, 245 andlayers 241, 251, 253 comprising semiconductor and dielectric layers toprovide transistor, capacitor and other drive circuitry elements. Asillustrated in FIGS. 6-7 via 242 is arranged to connect to electrode 234that in turn is contacted to rear reflector 240 that may for example bea silver electrode. Electron transport layer 236, emission layer 232,hole transparent electrode layer 238 and transparent electrode 244 isprovided on the electrode 234 to achieve the emitting pixel 220.

The pixel 220 is provided with well profile 272 with a central region273 that may be substantially planar and tilt regions 271 that aretilted and may further be provided with planar surfaces or curvedsurfaces.

Filler material 270 is provided between the tilt regions 271. The fillermaterial may for example have a refractive index of approximately 1.8.The refractive index of the filler material may be similar to therefractive index of the emission layer 232 material.

In operation, light rays are provided by source 269 that have an angulardistribution of luminous intensity that is determined by wavelength,reflections from reflective layer, interference between coherentwavefronts, guiding within layers and surface plasmon absorption in themetal layers. Such propagation properties are commonly referred to asmicrocavity emission effects.

In the present embodiments, light rays 276 are emitted towards thenormal direction are directly output without incidence at the outerregions 271 of the pixel 220. Light rays 274 are output after incidenceat the reflective layers of the tilt regions 271. Light rays 276 areguided within the filler material 270 and output after incidence of thetilt region 271.

Advantageously light rays 274, 276 that would be lost by guiding withinthe cover layer 246 are directed in the forwards direction. Incomparison to the arrangements described elsewhere, the parallax barrier700 may be omitted and cost reduced. In other embodiments, not shown theprofiled pixels of FIGS. 41-43 may be provided together with parallaxbarrier 700. Advantageously efficiency is increased and off-axis visualsecurity level increased for privacy mode of operation.

Returning to FIG. 42 , the profiles of the tilt regions 271 may bedifferent for red, green and blue pixels 220, 222, 224. Such differencesmay compensate for different colour roll-offs for microcavityinterference affects. Advantageously colour uniformity may be improved.

FIG. 44 is a schematic graph illustrating variation of luminousintensity for profiled and non-profiled OLED pixels. In comparison tothe profiles of luminance against polar angle, the profile of luminousintensity against lateral angle is given. Thus a Lambertian outputprofile 280 has a cos θ profile. The profile 282 for a conventional OLEDpixel is provided together with a desirable profiles 284, 286 that maybe provided by the profiled pixel 220 with tilt regions 271. Desirablythe luminous intensity at polar angles of at least 45 degrees is lessthan 15% of the maximum luminous intensity and preferably less than 10%of the maximum luminous intensity. Further the maximum luminousintensity at polar angles of at least 60 degrees is less than 7.5% ofthe maximum luminous intensity and preferably less than 5% of themaximum luminous intensity.

FIG. 45A is a polar plot array for the component contributions andoutput of the arrangement of FIG. 41 comprising polar plots for spatiallight modulator luminance of luminous intensity profile 286 in FIG. 44 ,switchable retarder transmission, switchable retarder reflection, publicmode luminance, privacy mode luminance and visual security level; andFIG. 45B is a linear profile plot array for the component contributionsand output of the arrangements of FIG. 45A comprising linear profiles atazimuthal angles of 0, 90, 45 and 225 degrees.

The profiled OLED pixels 220, 222, 224 are arranged to provide increasedhead-on luminance and reduced off-axis luminance. Advantageously visualsecurity level is increased for off-axis snoopers in a privacy mode ofoperation. Further output efficiency is increased for the head-on user.

It may be desirable to provide a display that provides a privacyfunction in landscape and portrait modes of operation.

FIG. 46 is a schematic diagram illustrating in side perspective view aswitchable privacy display device 100 for use in ambient illumination604 comprising an emissive spatial light modulator 48, a parallaxbarrier 700, a first polar control retarder 300A arranged between thedisplay polariser 218 of the emissive spatial light modulator 48 and afirst additional polariser 318A; and a reflective polariser 302 andsecond polar control retarder 300B arranged between the first additionalpolariser 318A and a second additional polariser 318B.

FIG. 47A is a schematic diagram illustrating in front perspective viewan arrangement polarisers and polar control retarders for the embodimentof FIG. 46 wherein the first and second polar control retarders arecrossed and the spatial light modulator comprises the parallax barrier700. In this embodiment, liquid crystal alignment in the switchablepolar control retarder 301A is provided by homeotropic alignment layerwith alignment direction 419AAz with pretilt direction 419AAy andhomogeneous alignment layer with pretilt direction 419AB, where thedirections 419AAy, 419AB are antiparallel; and liquid crystal alignmentin the switchable polar control retarder 301B is provided by homeotropicalignment layer with alignment direction 419BAz with pretilt direction419BAy and homogeneous alignment layer with pretilt direction 419BB,where the directions 419BAy, 419BB are antiparallel, and directions419AAy, 419AB are orthogonal to directions 419BAy, 419BB.

Features of the embodiment of FIG. 47A not discussed in further detailmay be assumed to correspond to the features with equivalent referencenumerals as discussed above, including any potential variations in thefeatures.

FIG. 47B is a graph illustrating a simulated polar profile of luminanceoutput of an emissive spatial light modulator without the barrierstructure 700 of FIG. 46 .

FIG. 47C is a graph illustrating a simulated polar profile oftransmission of the barrier structure of FIG. 2 of light from the pixelsof the emissive spatial light modulator. An illustrative example isprovided in TABLE 9 where the emissive spatial light modulator 48 andthe aligned parallax barrier 700 has an output luminance profile havinga full width half maximum that is at most 40 degrees.

TABLE 9 Parameter, x-axis direction Illustrative value Pixel 224 pitch20 microns Pixel 224 emitting width 10 microns Barrier aperture 702width 10 microns Barrier separation, d 20 microns

TABLE 10 In-plane LC layer 314 Additional Additional passive AlignmentPretilt/ alignment retardance passive retarder retarder 330 retardanceLayer type deg direction (range) 330 type (range) 419BB Homogeneous 2270 1250 nm 419BA Homeotropic 88 90 (700 nm~2500 nm) 330B NegativeC-plate −1000 nm (−400 nm to −2100 nm) 419AB Homogeneous 2 180 1250 nm419AA Homeotropic 88 0 (700 nm~2500 nm) 330A Negative C-plate −1000 nm(−400 nm to −2100 nm)

FIG. 47D is a graph illustrating a simulated polar profile oftransmission of the second polar control retarder of FIG. 47A and TABLE10 arranged between the first and second additional polarisers whereinthe electric vector transmission directions of the polarisers areparallel; FIG. 47E is a graph illustrating a simulated polar profile ofreflectivity of the second polar control retarder of FIG. 47A and TABLE10 arranged between a reflective polariser and the second additionalpolariser wherein the electric vector transmission directions of thepolarisers are parallel; FIG. 47F is a graph illustrating a simulatedpolar profile of the total reflectivity comprising the reflectivity ofFIG. 47E and TABLE 10 and the Fresnel reflectivity from the frontsurface of the display device; FIG. 47G is a graph illustrating asimulated polar profile of transmission of the first polar controlretarder of FIG. 47A and TABLE 10 arranged between the display polariserand the first additional polariser wherein the electric vectortransmission directions of the polarisers are parallel; and FIG. 47H isa graph illustrating a simulated polar profile of the logarithm of totaloutput luminance of the spatial light modulator and first and secondpolar control retarders of FIG. 47A.

FIG. 47I is a graph illustrating a simulated polar profile of thesecurity level, S of the arrangement of FIG. 47A, TABLE 9 and TABLE 10in privacy mode for an ambient illuminance measured in lux that is twicethe head-on display luminance measured in nits. Advantageously anemissive display may be provided with a polar profile of security levelthat is desirable for both landscape and portrait operation.

FIG. 47J is a graph illustrating a simulated polar profile of thesecurity level, S of the arrangement of FIG. 47A, TABLE 9 and TABLE 10in privacy mode for an ambient illuminance measured in lux that is twicethe head-on display luminance measured in nits. In public mode, theoutput is determined by the profile 47B multiplied by the profile 47C.Security factor is illustrated in FIG. 47J. Advantageously securityfactor, S is less that 0.1 over a wide polar angular range so that animage can be clearly seen on the display.

As alternatives to the embodiment of TABLE 10, the retardances andalignment layers of the first and/or second polar control retarders301A, 301B may be provided by two homogeneous alignment layers or twohomeotropic alignment layers. In comparison to the arrangement of TABLE10, the polar range for high security factor and the resilience toapplied pressure may be modified to achieve desirable alternativecharacteristics.

As may be used herein, the terms “substantially” and “approximately”provide an industry-accepted tolerance for its corresponding term and/orrelativity between items. Such an industry-accepted tolerance rangesfrom zero percent to ten percent and corresponds to, but is not limitedto, component values, angles, et cetera. Such relativity between itemsranges between approximately zero percent to ten percent.

While various embodiments in accordance with the principles disclosedherein have been described above, it should be understood that they havebeen presented by way of example only, and not limitation. Thus, thebreadth and scope of this disclosure should not be limited by any of theabove-described exemplary embodiments, but should be defined only inaccordance with any claims and their equivalents issuing from thisdisclosure. Furthermore, the above advantages and features are providedin described embodiments, but shall not limit the application of suchissued claims to processes and structures accomplishing any or all ofthe above advantages.

Additionally, the section headings herein are provided for consistencywith the suggestions under 37 CFR 1.77 or otherwise to provideorganizational cues. These headings shall not limit or characterize theembodiment(s) set out in any claims that may issue from this disclosure.Specifically and by way of example, although the headings refer to a“Technical Field,” the claims should not be limited by the languagechosen under this heading to describe the so-called field. Further, adescription of a technology in the “Background” is not to be construedas an admission that certain technology is prior art to anyembodiment(s) in this disclosure. Neither is the “Summary” to beconsidered as a characterization of the embodiment(s) set forth inissued claims. Furthermore, any reference in this disclosure to“invention” in the singular should not be used to argue that there isonly a single point of novelty in this disclosure. Multiple embodimentsmay be set forth according to the limitations of the multiple claimsissuing from this disclosure, and such claims accordingly define theembodiment(s), and their equivalents, that are protected thereby. In allinstances, the scope of such claims shall be considered on their ownmerits in light of this disclosure, but should not be constrained by theheadings set forth herein.

The invention claimed is:
 1. A method to form a display device,comprising: forming an array of emissive pixels on a backplane bydirecting emissive materials through a fine metal mask; forming anencapsulation layer on the array of emissive pixels comprising at leastone transparent inorganic layer; and forming the parallax barriercomprising an array of apertures on the surface of the encapsulationlayer by one of directing light absorbing material through a fine metalmask, or lithographic patterning; wherein each emissive pixel is alignedwith a respective aperture in the array of apertures with a one-to-onecorrespondence.
 2. A method according to claim 1, wherein the parallaxbarrier is separated from the pixel layer by a parallax distance alongan axis along a normal to the plane of the pixel layer.
 3. A methodaccording to claim 1, wherein the pixels have a pitch p along thedirection in which the apertures are closest, the material between theparallax barrier and the pixels has a bulk refractive index n and theencapsulation layer has a thickness d meeting the requirement that2d/p≤√(2n²−1).
 4. A method according to claim 1, wherein the apertureshave a width a along the direction in which the apertures are closest,the material between the parallax barrier and the pixels has a bulkrefractive index n and the encapsulation layer has a thickness d meetingthe requirement that d≥an√(1−3/(4n²))/√3.
 5. A method according to claim1, wherein, along the direction in which the apertures are closest, theapertures have a width a and the pixels have a width w meeting therequirement that a≥w.
 6. A method according to claim 1, wherein, alongthe direction in which the apertures are closest, the apertures have awidth a, the pixels have a pitch p and the pixels have a width w meetingthe requirement that a≤(p−w/2).
 7. A method according to claim 1,wherein the parallax barrier has a separation d from the pixels and theapertures have a width a along the direction in which the apertures areclosest and material between the parallax barrier and the pixels has arefractive index n meeting the requirement that d≥a√(n²−1)/2.
 8. Amethod according to claim 1, wherein the parallax barrier has aseparation d from the pixels and the apertures have a width a along thedirection in which the apertures are closest and material between theparallax barrier and the pixels has a refractive index n meeting therequirement that d≥an√(1−3/(4n²))/√3.
 9. A method according to claim 1,wherein the parallax barrier forms a two-dimensional array of apertures.10. A method according to claim 1, further comprising forming anadditional layer between the array of emissive pixels and the parallaxbarrier, wherein the array of emissive pixels, the additional layer, andthe parallax barrier are formed as a monolithic stack.
 11. A methodaccording to claim 10, wherein the additional layer comprises a lighttransmitting inorganic layer arranged to provide a barrier to water andoxygen.
 12. A method according to claim 11, wherein the parallax barrieris arranged between the array of emissive pixels and the lighttransmitting inorganic layer that is arranged to provide a barrier towater and oxygen.
 13. A method according to claim 1, wherein theparallax barrier comprises a light transmitting inorganic materialarranged to provide a barrier to water and oxygen.
 14. A methodaccording to claim 1, wherein the emissive pixels comprise lightemitting diodes.
 15. A method according to claim 14, wherein the lightemitting diodes are organic light emitting diodes comprising an organiclight emitting material.
 16. A method according to claim 1, wherein thearray of apertures is formed on a touch sensor electrode array.
 17. Amethod to form a reflectivity control display device, comprising:forming an array of emissive pixels on a backplane by directing emissivematerials through a fine metal mask; forming an encapsulation layer onthe array of emissive pixels comprising at least one transparentinorganic layer; and forming the parallax barrier comprising an array ofapertures on the surface of the encapsulation layer; wherein eachemissive pixel is aligned with a respective aperture in the array ofapertures with a one-to-one correspondence.
 18. A method according toclaim 17, wherein the parallax barrier is separated from the pixel layerby a parallax distance along an axis along a normal to the plane of thepixel layer.
 19. A method according to claim 17, wherein the pixels havea pitch p along the direction in which the apertures are closest, thematerial between the parallax barrier and the pixels has a bulkrefractive index n and the encapsulation layer has a thickness d meetingthe requirement that 2d/p≤√(2n²−1).
 20. A method according to claim 17,wherein the apertures have a width a along the direction in which theapertures are closest, the material between the parallax barrier and thepixels has a bulk refractive index n and the encapsulation layer has athickness d meeting the requirement that d≥a√(n²−1)/2.
 21. A methodaccording to claim 17, wherein forming the parallax barrier comprisingan array of apertures on the surface of the encapsulation layer is bydirecting light absorbing material through a fine metal mask.
 22. Amethod according to claim 17, wherein forming the parallax barriercomprising an array of apertures on the surface of the encapsulationlayer is by lithographic patterning.